Add openapi spec for new SOGS API

[jagerman]

TODO:

• room ban list retrieval (for moderators/admins). Should be extensible in the future so that we can add fields (e.g. User-viewable ban reason #32 ) to rows without breaking the response structure.
• room permission override retrieval so that moderators can view overrides to remove/update them.
• Similar endpoints for global bans/permission overrides.
• Endpoint to access list of global moderators/admins (we have this for rooms already, but not global mods).
• Define generic error responses that can get returned from any endpoint.

[jagerman]

(Current version, as of this post, is viewable view a tool such as: https://redocly.github.io/redoc/?url=https://jagerman.com/api.yaml)

[jagerman]

Merging into dev, which we can continue to amend with future PRs before it gets merged into a stable release.