Re-organize to not have a non-diataxis docs/source/topic folder

[consideRatio]

We have a folder that includes non-diataxis (https://diataxis.fr) written content. I think we should perhaps discard some of that unless it finds a better home within the diataxis framework categories of how-to/tutorials/explanation/reference.

• There are github.md writing about github specific scopes.
• There gitlab.md writing about gitlab specific scopes.
• There is google.md writing about how to do some pre-requisite things to configure group based authorization and such

I think the scopes parts may be too specific, and that the google thing may belong to the how-to section for using GoogleOAuthenticator, perhaps split apart to tightly scoped google specific how-to docs.