Changes for v2 content libs

[ormsbee]

Work to support https://github.com/openedx/edx-platform/pull/34066

This bumps the version for openedx-learning to 0.5.0.

Some highlights:

• new API functions and queries needed for draft/publish comparisons, fetching & creating component versions, etc.
• re-created the migrations yet again, since this is the last time I should be able to get away with it before it gets installed into edx-platform.
• made some fixes that I realized would bite us later (like making the text collation text insensitive for search purposes later).
• new custom manager to make it easier to specify common "select_related" queries on models, first used on Component.
• a few performance tweaks based on looking at the queries that show up when using this in edx-platform in https://github.com/openedx/edx-platform/pull/34066 (mostly getting rid of n+1 queries)

Squashed commit message:

This commit adds a number of features needed to accomodate content
libraries. These are all collected together because this work was done
while iteratively making more and more of libraries functional, and it
was difficult to properly separate out later.

This bumps the version to 0.5.0.

New publishing API functions:

* Learning Packages
    * get_learning_package
    * get_learning_package_by_key,
    * update_learning_package

* Publishable Entities
    * get_publishable_entity and
    * get_publishable_entity_by_key

* Draft/Publishing
    * get_last_publish
    * get_all_drafts
    * get_entities_with_unpublished_changes
    * get_entities_with_unpublished_deletes
    * get_published_version
    * set_draft_version
    * soft_delete_draft
    * reset_drafts_to_published

New Components API functions:

* create_next_version
* get_component_by_key
* component_exists_by_key
* get_components

PublishableEntityMixin improvements:

* New property methods: latest, has_unpublished_changes
* Existing methods were improved to use model-cached values.

Encoding fixes:

* collations for multiple fields were changed to be case insensitive in
  order to better support simple text searches.

Model optimizations:

* created the WithRelationsManager to more easily define querysets that
  involve adding select_related fields. This was used to elininate a
  number of n+1 queries that came up during libraries development.
* PublishableEntityVersion.version_num was reduced to a 4-byte
  PositiveIntegerField instead of using the 8-byte default for
  openedx_learning apps (it's assumed we will never make more than 2
  billion versions of a particular PublishableEntity). This was done to
  help reduce the size of indexes.

Typing:

* type annotations were added to many functions and test functions.

[ormsbee]

Okay, I think I've gotten all the basic changes in there. Now to fix old tests and add new ones for the new functionality. Then a final re-base and version bump.

[ormsbee]

Old tests are fixed, added a few new ones, still some more to go. I'll deal with mypy last.

[ormsbee]

@kdmccormick, @bradenmacdonald: If you have some time, please give this a review pass. The tests aren't fully there yet, but I'd appreciate your thoughts on the API additions especially.

[ormsbee]

Okay, I wrote the tests, made changes based on the review comments, and the linters are appeased. I'm going to do the _pk refactoring now, but with any luck I'm hoping this can merge today.

[ormsbee]

Okay, slight delay because I noticed that it's always doing the work of loading all components no matter the pagination params in the REST API. I think this is a problem on the edx-platform side, but I'm looking into it to be sure.

[ormsbee]

Okay, I wrote the tests, made changes based on the review comments, and the linters are appeased. I'm going to do the _pk refactoring now, but with any luck I'm hoping this can merge today.

I went back and forth on _id vs. _pk for a bit and then decided to punt entirely by making these arguments positional-only for the moment. >_<

[ormsbee]

Also, I tracked down the query issue to something in edx-platform, and I'll have an update for that PR with the fix later. Part of it points to an issue that our internal APIs have with QuerySets and pagination. Namely, the pattern for DRF and Django in general is QuerySet -> Pagination -> Serialization. So it gets awkward when we're returning something from an API that we want to be QuerySet-like in that it's filterable and pageable, but also presents something that is not actually a model. I hacked up something before that wrapped the __iter()__ call and did serialization that seemed to work, but I feel like that's probably too much hackery to want to support in the longer term.

Anyhow, I'll discuss it more on the other PR.

[ormsbee]

It occurred to me while looking at some recent comments in the wiki w.r.t. library content needs that we probably want to have ComponentType represented as its own model. Partly for saving space, but mostly because it gives us something to later hang policy off of on a per-type basis, e.g. "videos are okay to show in libraries, SGA blocks are experimental for library use".

I implemented that this evening. It was pleasantly straightforward, and it also gets rid of our having to tell pylint to ignore our use of type as a variable name. Tests already pass, so hopefully I can just do it as a fast-follow to this PR tomorrow if this merges.

[ormsbee]

BTW, the only reason this build isn't green is because I was a doofus and mis-spelled a couple of conventional commit messages. Please know that it's ready for final review, and I'll squash it at the end.

[bradenmacdonald]

Question that's not directly related: Can you use add_content_to_component_version to modify a ComponentVersion that has already been published?

[ormsbee]

Thanks folks! I squashed my commits and made a decent commit message out of it. Will merge once things are green.

[ormsbee]

Question that's not directly related: Can you use add_content_to_component_version to modify a ComponentVersion that has already been published?

Yes, you can. 95% of the time you shouldn't, but some real use cases came up where doing so seems like it would be beneficial:

• Bug fixes: We expect people to attach data to ComponentVersions, but that code will have bugs at some point, and people will want to be able to correct that programmatically without creating a new "version" of that thing.
• Data upgrade/migration: Say we have tens of thousands of Videos with SRT files, and we want to bulk upgrade everything to VTT files instead. We'd probably update the player to recognize both (with a preference for VTT), and then bulk convert SRT to VTT where VTT is absent.