Adds Python API documentations for gpu.capabilities module. Ref D12226
While doxygen supports both, conform to our style guide. Note that single back-tick's are already used in a majority of comments.
This module exposes the capabilities defined in the GPU module in C. This will be useful for porting existing code in `bgl` to `gpu`. Reviewed By: fclem, brecht, campbellbarton Maniphest Tasks: T80730 Part of D11147