Implement to show the message with `--help`

[peacock0803sz]

Implement of #2263, Showing deprecation message with --help for @click.option

• fixes #2263

Checklist:

• [x] Add tests that demonstrate the correct behavior of the change. Tests should fail without the change.
• [x] Add or update relevant docs, in the docs folder and in code.
• [x] Add an entry in CHANGES.rst summarizing the change and linking to the issue.
• [x] Add .. versionchanged:: entries in any relevant code docs.
• [x] Run pre-commit hooks and fix any issues.
• [x] Run pytest and tox, no tests failed.

[saroad2]

Hello @peacock0803sz , thanks for the PR and sorry for the long delay.

This seems fine to me, and very helpful for user to use click in a backward compatible way.

However, this PR lacks a very important compnant: Once someone does use a deprecated option, a warning should be printed. This is done today with deprecated commands. You can look here for inspiration.

Please fix this issue before I review this PR again.