[DevEx] Improve usefulness of commit messages by standardizing formatting and expectations

[joshuarrrr]

Is your feature request related to a problem? Please describe.

This has come up a few times in the context of our discussions about CHANGELOG.md and release note generation (#591, #2189, #2677):

• See [PROPOSAL] Introduce in automatically generated release notes #2677 (comment) (and subsequet responses)
• Also mentioned by @kristenTian in [Maintenance] Exempt feature branches from changelog verification #3123 (comment)

Describe the solution you'd like

We can provide a git commit template (commit.template), along with a git hook that enforces the format. Even better would be a hook that interactively guides the contributor to provide enough context in the commit. The tooling should focus on the fidelity of the description, and be able to silently correct minor formatting errors.

The commit template should also be compatible with and complementary to whatever PR templates we have - the idea is to do the hard work of describing the changes, reasons, and impacts just once, and then leverage that high quality description elsewhere (PR description, CHANGELOG, etc.). See additional context.

Describe alternatives you've considered

We could also have enforcement of commit formatting in a GitHub workflow. But it's annoying to only find out that you had an improperly formatted commit after you've pushed a PR. Relying on maintainers to manually enforce on every PR also sounds exhausting and unreasonable.

Additional context

From @seraphjiang:

The effort to ensure high quality commit message for PR and high quality for change log message are same. To save effort, we should focus on ensure high bar on commit message anyway.