[Docs] Add docs with mkdocs

[smokestacklightnin]

Google Would like to migrate the documentation for mlmd away from their internal systems, so this PR implements that migration.

Changes in this PR:

• Add .gitignore to the project
• Add mkdocs to the dependencies and add a configuration for it
• Add a GitHub workflow to deploy the documentation on GitHub Pages
• Add __all__ variables so modules and their members are recognized by mkdocs
• Fixed notes admonitions
• Add white background to rendered png images so they are legible in dark mode

TODO:

• Fix the triggers before merge
• Find a solution for including members of the proto submodule

[peytondmurray]

I made a few additional changes:

• Renamed g3doc -> docs, since we are no longer using internal tooling for building documentation and docs is the standard mkdocs documentation directory
• Modified the .gitignore to include bazel-* build artifacts
• Updated the workflow to build docs on python 3.12
• Enabled building and publishing docs on pushes to master

[peytondmurray]

This isn't in scope for this PR, but the try/except block above doesn't work. In the event of an ImportError, this module won't be able to export these symbols. I can't really tell what is intended by the try/except block swallowing any import errors, but maybe this is something we can clean up in a future PR.

[smokestacklightnin]

This seems to have been present since before we started working on the repo.

I agree with you that we can possibly revisit this in a future PR

[peytondmurray]

If you're going to remove the del metadata_store_pb2 line, can you also remove these other two?

Just a note of context for others working on this: I'm assuming this is to "un-import" the imported protobuf modules...but I'm not clear on why this is needed. If the goal is to re-export certain symbols, from <module> import <symbol> is sufficient. del <module> doesn't "un-import" the module - it persists elsewhere. See https://mail.python.org/pipermail/tutor/2006-August/048596.html for details.

[smokestacklightnin]

I removed del metadata_store_pb2 because as it is currently written, it is not imported directly anymore. It just has member objects imported. I left the other two del statements because they are not used to import member objects. My preference is to leave them as they are and revisit them in the future.

[peytondmurray]

A few minor changes/questions. Once those are done, if you've checked that this deploys and looks good, then let's ship it! 🚢

[smokestacklightnin]

@peytondmurray I think we should allow this to run for push on any branch so developers can preview the deployment from their forks. If we make the reasonable assumption that nobody is pushing directly to upstream/master, then this will not affect the main docs deployment.

[peytondmurray]

Right now we have no way of deploying builds of individual branches - for now it is up to the users to build the docs and examine their changes locally, and for reviewers to pay due diligence in asking PR authors to provide screenshots/description of major changes to the docs.

Nobody will be pushing to master, but we still want this enabled so that when github itself makes a merge commit and pushes it to master the docs will be rebuilt. As it stands every PR will force-push to gh-pages.

[smokestacklightnin]

@peytondmurray fixed merge conflict and marked as ready for review

[peytondmurray]

Thanks for this 🚀

[XinranTang]

Hi, could you please resolve the conflicts in this branch?

[smokestacklightnin]

Hi, could you please resolve the conflicts in this branch?

Done

CC: @peytondmurray