Update unstable endpoints from i.e xyz.amorgan/knock -> xyz.amorgan.knock

I'm doing this for two reasons:

1) If I ever wanted to create another knock-related MSC, it would be nice to be able
to give it a different namespace for endpoints, such as xyz.amorgan.knock2/knock. If
we were only using xyz.amorgan as the namespace for endpoints, that restricts that
namespace to only work for one MSC which attempts to use /knock as part of an endpoint.

2) I accidentally made the implementation use xyz.amorgan.knock/knock :)

proposals/2403-knock.md

@@ -629,17 +629,17 @@ implementation. The unstable counterpart for each endpoint is:
 C-S knock:
 
 * `POST /_matrix/client/knock/{roomIdOrAlias}`
-* `POST /_matrix/client/unstable/xyz.amorgan/knock/{roomIdOrAlias}`
+* `POST /_matrix/client/unstable/xyz.amorgan.knock/knock/{roomIdOrAlias}`
 
 S-S make_knock:
 
 * `GET /_matrix/federation/v1/make_knock/{roomId}/{userId}`
-* `GET /_matrix/federation/unstable/xyz.amorgan/make_knock/{roomId}/{userId}`
+* `GET /_matrix/federation/unstable/xyz.amorgan.knock/make_knock/{roomId}/{userId}`
 
 S-S send_knock:
 
 * `PUT /_matrix/federation/v1/send_knock/{roomId}/{eventId}`
-* `PUT /_matrix/federation/unstable/xyz.amorgan/send_knock/{roomId}/{eventId}`
+* `PUT /_matrix/federation/unstable/xyz.amorgan.knock/send_knock/{roomId}/{eventId}`
 
 Finally, an unstable prefix is added to the key that comes down `/sync`,
 the join rule for rooms and the `content.membership` key of the member