[IVT-2794] Adding fix for handling two tags to same revision

[uwaheed88]

Issue: IVT-2794

• Update in blueprint.py and helper.py to add tag_name in the request parameter of version URL.
• Update in plugin.py to fetch the tag name from the request URL parameter and used to filter current_version on the basis of revision_ref and tag_name.

This resolves #49

[shevron]

I realize now that this takes more design work and solving it right may be slightly more complex than what has been initially communicated.

I don't think our solution should change any URL structures, and I don't think it should be a superficial change. This is something deeper, and may even require a (small) fix to metastore-lib to handle. What I want is this:

1. The revision_ref parameter in URLs can specify either a revision ID (typically a sha1 or sha256) or a tag name.
2. This parameter is passed as-is all the way down to metastore-lib which already makes the distinction between the two by itself when storage.fetch() is called.
3. Either on the metastore-lib level (which currently will not return any extra information depending on whether a tag or a revision was fetched), or on the ckanext-versioning action level, we put some additional metadata on the revision or tag into the fetched package dict, or we put this information into the context. We can then use this information when rendering templates.

Note that metastore-lib already provides some methods of telling between a revision ID and a tag name, and we can just re-use those in ckanext-versioning if needed. It may even make sense for storage backends to expose a new method, something like is_valid_revision_id(revision_ref: str) -> bool to allow consuming code to check if something will be treated by the storage backend as if it was a revision ID or a tag (anything that is not a valid revision ID is assumed to be a tag).

Let me know if you want to further discuss this and come up with a design together.

[uwaheed88]

@shevron Can you approve now as the tests have now passed?

[shevron]

Tested locally, works well. As a bonus, using the revision ID in the URL also works. 👍 Good job.