* C2S: Deprecate now-legacy endpoints
* C2S: Fix MXC URI code block while we're here
* C2S: Describe the authentication and deprecation requirements
* C2S: Intro the upload/download endpoints differently
* C2S: Literally copy/paste the `content-repo.yaml` spec
* C2S: Drop `/upload` and `/create` because we aren't replacing them today
* C2S: Fix notes while we're here
* C2S: Update metadata for new endpoints
* C2S: Add authentication to new endpoints
* C2S: Drop `allow_remote` and `allow_redirect` on new endpoints
* C2S: Append backwards compatibility notes
* C2S: Decorate old media endpoints with pointers to the new ones
The server-server spec might have a harder time linking to these, but that can be fixed with verbiage.
* C2S: Annotate IdP icon spec with media auth implications
* S2S: Modernize section text
* S2S: Create content repository API
This is largely a copy/paste of the new authed content repo API in the Client-Server API, though some keywords (like "client") have been changed. Paths and response formats have also been changed to support the federation-specific requirements.
* C2S & S2S: Add plethora of changelogs
* Reference RFC 1341
* Upgrade keywords in changed text
* Mention caching
* Cross-reference IdP icons
* Update content/client-server-api/modules/content_repo.md