Add admonitions with expected Godot support

Cyril Bisseyrequested to merge
admonitions into main

Admonitions have been in the works in Godot PR 63079 for a while, and will hopefully be added Soon™. This adds support for important, note, tip, and warning admonitions, with the option to change those to target specific formats/SSGs (e.g. replacing important with info).

Merge request reports