Implement `schemas.list` RPC method

[seancolsen]

Fixes #3596

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[seancolsen]

Note this is stacked on top of #3597

[seancolsen]

Ready for re-review, @mathemancer

[Anish9901]

@seancolsen I noticed that this PR doesn't have any python test for testing the schemas.list_ rpc function, it only has one for testing the expected name of the endpoint. Any reason why that may be?

[seancolsen]

@Anish9901 It didn't seem worth testing to me. Do you think it should have a test? What would you want to assert in that test? I'm open to it certainly. But also trying to avoid too much boilerplate in order to move quickly. For reference, we discussed this in our last meeting (starting at about 48:20 and my take-away from that discussion was that the test coverage that matters the most to us right now is the test coverage at the SQL layer.

[Anish9901]

Ok, I just went through the video, as per my understanding, I don't think we agreed on not adding the python tests for the rpc endpoints rather I think we decided on not having end-to-end python tests which would call up the db and hence tend to be slow. FWIW, I think we should at least have one test for making sure that the sql function is called with appropriate parameters, this is relatively low effort. I'd like to hear @mathemancer's opinion on whether or not we want tests that check the wiring of the functions that are called from within the rpc functions.

[mathemancer]

As I'm looking through the PR with @Anish9901 's concerns in mind:

• Given that we're not doing any E2E or even full-backend-call testing, we need to be extra conscientious about testing that the wiring between tests is as expected, and that tests are mangling things appropriately.
• For the schema listing RPC function, therefore, we could add a test to:
  • Make sure the call to the underlying python-layer function is as expected, and
  • The list comprehension produces expected output, given some monkeypatched result from the python-layer function.

This would be similar to, for example, the test for columns.list_. It's kind of a pain to put together, but it does give us something to break if we accidentally typo something in the function logic that we might not otherwise notice.