Support fixme's in docstrings

[badsketch]

Type of Changes

	Type
	:bug: Bug fix
✓	:sparkles: New feature
	:hammer: Refactoring
	:scroll: Docs

Description

Closes #9255

Previous PR discussion here: https://github.com/pylint-dev/pylint/pull/9281

• now an enhancement of existing fixme rather than a new message
• check-fixme-in-docstring is the setting that enables it and defaults to false
• also suggestions to improve the existing description: https://github.com/pylint-dev/pylint/pull/9281#discussion_r1415102708. I kind of like how the message is the TODO itself. As for the "Used when a warning note..." is that for a tooltip? I believe almost all checker messages have something like this, right?

Appreciate any feedback!