Change Default Room version to 10 (#2933)

This PR implements
[MSC3904](matrix-org/matrix-spec-proposals#3904).
This PR is almost identical to #2781 but this PR is also filed well
technically 1 day before the MSC passes FCP but well everyone knows this
MSC is expected to have passed FCP on monday so im refiling this change
today on saturday as i was doing prep work for monday. I assume that
this PR wont be counted as clogging the queue since by the next time i
expect to be a work day for this project this PR will be implementing an
FCP passed disposition merge MSC.

Also as for the lack of tests i belive that this simple change does not
need to pass new tests due to that these tests are expected to already
have been passed by the successful use of Dendrite with Room version 10
already.

### Pull Request Checklist

* [X] I have added tests for PR _or_ I have justified why this PR
doesn't need tests.
* [X] Pull request includes a [sign
off](https://github.com/matrix-org/dendrite/blob/main/docs/CONTRIBUTING.md#sign-off)

Signed-off-by: Catalan Lover <catalanlover@protonmail.com>

Co-authored-by: Till <2353100+S7evinK@users.noreply.github.com>
Co-authored-by: kegsay <kegan@matrix.org>

roomserver/version/version.go

@@ -23,7 +23,7 @@ import (
 // DefaultRoomVersion contains the room version that will, by
 // default, be used to create new rooms on this server.
 func DefaultRoomVersion() gomatrixserverlib.RoomVersion {
-	return gomatrixserverlib.RoomVersionV9
+	return gomatrixserverlib.RoomVersionV10
 }
 
 // RoomVersions returns a map of all known room versions to this