GET /schemas and its configs are undocumented

[kevin-cantwell]

We were upgrading schema registry and discovered that a new behavior was introduced to the GET /schemas endpoint. Specifically from this PR which, afaict, was introduced in version 7.4.x.

The new behavior limits the number of schemas returned by default. This behavior is not documented in the api reference. In fact the GET /schemas endpoint is entirely missing from the docs.

I've published the swagger docs from the 7.6.x branch here, to better see the full documentation. As far as I can tell, this isn't published anywhere on the confluent site.