Docs: add esbonio for preview/linting of sphinx documentation

[AlexanderLanin]

Part 1 of #30:
Introduce initial highlighting, preview and linting for .rst and .md files (-> esbonio)

New dependency aspect_rules_py is Apache-2.0 Licensed

[MaximilianSoerenPollak]

Looks good to me.
These are changes we had in the other repository and there they worked as expected. 👍

[AlexanderLanin]

CI is not considered here. I'd rather implement that in combination with PR-based previews of the documentation in a separate PR.

[AlexanderLanin]

Issue-ref
Bug in gitlint: The check does not match contribution guidelines. Body does not have to reference an issue anymore.
--> #117

title-match-regex
My goal was to squash the commits here in the Web UI and adapt the commit heading at that point. However I cannot do that, since merge is blocked. So I basically have to adapt my commits... which will not end up in the history anyway!
And note: once I do that, I might loose the prefix, even if all commits had one ⚠️

[AlexanderLanin]

Squashed + rebased + commit msg adjusted.