Set room version default to 5

changelog.d/6220.feature

+Increase default room version from 4 to 5, thereby enforcing server key validity period checks.

docs/sample_config.yaml

@@ -72,7 +72,7 @@ pid_file: DATADIR/homeserver.pid
 # For example, for room version 1, default_room_version should be set
 # to "1".
 #
-#default_room_version: "4"
+#default_room_version: "5"
 
 # The GC threshold parameters to pass to `gc.set_threshold`, if defined
 #

synapse/config/server.py

@@ -41,7 +41,7 @@ logger = logging.Logger(__name__)
 # in the list.
 DEFAULT_BIND_ADDRESSES = ["::", "0.0.0.0"]
 
-DEFAULT_ROOM_VERSION = "4"
+DEFAULT_ROOM_VERSION = "5"
 
 ROOM_COMPLEXITY_TOO_GREAT = (
     "Your homeserver is unable to join rooms this large or complex. "