Add possible values in the doc

[PitiBouchon]

Add the different possible values the doc for non trivial config

[PitiBouchon]

Just adding the possible values so that people can find them on manual configuation instead of looking in the code

[bors]

:umbrella: The latest upstream changes (presumably #16639) made this pull request unmergeable. Please resolve the merge conflicts.

[Veykril]

I'll close this. While we definitely want to tackle this, it should be ideally be derived from the types somehow, otherwise this will get out of sync rather easily. https://github.com/rust-lang/rust-analyzer/issues/13178 tracks this and once we are done revamping the configs we can tackle it.