TensorBoard 2.12.0

[arcra]

• Motivation for features / changes
  The TensorBoard release that tracks the TF 2.12 release.

• Technical description of changes

  • Fixes a test related to our "compat" proto copies to keep in sync with TF protos.
  • Updates our "compat" proto copies from the TF repo up to the branch cut commit for their release 2.12 (3e5b6f1899f8515b3f27c67b5bea7481e990c163).
  • Adds the normal release commits to:
    • pin the TF version for CI (to tf-nightly==2.12.0.dev20230201, which is the one available before the branch cut commit),
    • add release notes, and
    • bump the TB version.

• Detailed steps to verify changes work correctly (as executed by you)
  Generated the pip package and ran it to test that it works. There is a known issue still, with the WhatIfTool plugin, which is a separate pip package that we use, and which needs to update their proto dependency as well, but to unblock the TF release, we'll deal with that later. The rest of the functionality of TB is unaffected.

[nfelt]

LGTM to rebase and merge - thanks! 🦀 🎉

[arcra]

As discussed in person, I removed some lines from our CI workflow where we were generating a pip package with a PEP 440 non-conforming name, which setuptools doesn't support since version 66.

That package was not used, so there are no consequences for this release.