[CI] Ensure messages.pot stays updated

[Chaitanya-Keyal]

Description

This PR introduces a new CI job to ensure that the messages.pot file is always up to date. It also adds a pre-commit hook that automatically runs the extract_messages step before each commit.

Pre-commit hook

The hook runs a Python script that does the following:

• Runs python3 setup.py extract_messages.
• Checks if the updated messages.pot differs from the previous version, ignoring changes to the metadata fields POT-Creation-Date and Generated-By.
• If there are meaningful changes, the hook ends with a "failed" status because it modified tracked files (this is expected). The developer can then review and commit the updated messages.pot.
• If the only differences are in the ignored metadata fields, the file is reverted to its previous state, preventing unnecessary diffs.

Github Action

Similarly, the GitHub workflow runs the pre-commit hook. If it results in any changes, they will appear as a diff in the logs, and the action will fail. This makes it clear that the PR must be updated to include the corresponding changes to messages.pot.

Other changes

• Added setuptools as a dependency in requirements-l10n.txt.
• Updated messages.pot since the dev branch was not up to date.
• Updated documentation with instructions for setting up the pre-commit hook.

I also considered adding pre-commit itself to requirements-l10n.txt, but decided against it. It’s not strictly an l10n dependency. We may want to add a requirements-dev.txt instead, or even better, migrate fully to pyproject.toml and/or a tool like uv.

---

This pull request is categorized as a:

• Other

Checklist

• I’ve run pytest and made sure all unit tests pass before submitting the PR

If you modified or added functionality/workflow, did you add new unit tests?

• N/A

I have tested this PR on the following platforms/os:

• Other

[newtonick]

LGTM, ACK and Tested locally and in my forked repo with some test PRs.