FastAPI route for remote files

[davelopez]

Ref #10889

Summary

• Added RemoteFilesManager to encapsulate the controller logic.
• Created the pydantic models
• Added the new FastAPI endpoints

Additional comments

• I have added some Enums to control the possible values as the /api/remote_files index method docstrings suggested. This provides validation and shows them in the interactive OpenAPI docs as a nice combo. After that, I realized that the target query parameter can be also a URI so ended up leaving it as an str.
• The FilesSourcePlugin pydantic model tries to represent the base of any kind of files source plugin. To allow other types of plugins (e. g. dropbox, etc.) to add their own fields to the serialization, and do not break the validation, a little extra configuration was added to this model.

[jmchilton]

This is lovely - a very solid refactoring that was on my todo list.

[davelopez]

Many thanks!

[jmchilton]

The CircleCI test is broken in dev (working on it) but there is an outside chance that integration selenium test failure might intersect this code so I'm re-running that test.

[jdavcs]

The CircleCI test is broken in dev (working on it) but there is an outside chance that integration selenium test failure might intersect this code so I'm re-running that test.

I had the same failures (mypy errors in packages + integrated selenium test) on my PR after a green run. Unless this is different, it should be unrelated to the PR.

[davelopez]

Thank you @jmchilton and @ic4f for checking. I managed to run the failing test locally and seems to pass.
Let's check it again after the weekend when the CI has had some proper rest 😄

[jmchilton]

Yeah - hopefully #11217 helps track down those integration selenium failures.