Add registration token UIA type (#3616)
* Add registration token UIA type
MSC: https://github.com/matrix-org/matrix-doc/pull/3231
**Note**: This introduces the endpoint as v1 rather than r0 given the global versioning changes landed between the acceptance of the MSC and now.
* Fix swagger
* Changelogs
* Update data/api/client-server/registration_tokens.yaml
Co-authored-by: Hubert Chathi <hubert@uhoreg.ca>
Co-authored-by: Hubert Chathi <hubert@uhoreg.ca>
