Please, document a workflow on the support of new GHCs

[Anton-Latukha]

Support of new versions is a constant periodic task.

Denoting main steps/phases would allow for reports as #2541 & for maintainers & users to be more context-aware of the process. So the tracking reports created would have a more stable form & the process would be easier to track.

[Anton-Latukha]

The placing is somewhere nearby: https://haskell-language-server.readthedocs.io/en/latest/supported-versions.html

The theme is interconnected with https://haskell-language-server.readthedocs.io/en/latest/contributing/releases.html.

[Anton-Latukha]

Since I need to #2525 anyway - I would go into some doc PR mode. Would do a bunch of doc pattern work. Like, open a minimal PR adding 9.0.2 information & ghcup dependency-aware description of GHC support process information from #2541.