Clean up RTD docs

[felixwang9817]

There are several issues with the RTD docs right now:

First, there is no way to confirm whether the RTD docs will build correctly. For example, the v0.23.2 docs did not render correctly, but this issue was not caught until a few days later. It was fixed by #3123, but there should be GH workflow that tests RTD docs during PRs and on master.

Second, the current RTD docs generate a lot of warnings when being built (run make html from feast/sdk/python/docs). There are several different kinds of warnings.

• For example, there is a WARNING: duplicate object description warning that is probably due to this issue with sphinx/napoleon. I haven't found a simple fix for this yet.
• There are also a bunch of warnings due to various docstrings in our codebase not conforming to the Google style guide (e.g. something like WARNING: Block quote ends without a blank line; unexpected unindent.). We should (a) fix our docstrings and (b) add a GH workflow that checks for these warnings.

[stale]

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