Ratelimit invites by room and target user (#9258)

docs/sample_config.yaml

@@ -825,6 +825,8 @@ log_config: "CONFDIR/SERVERNAME.log.config"
 #     "remote" for when users are trying to join rooms not on the server (which
 #     can be more expensive)
 #   - one for ratelimiting how often a user or IP can attempt to validate a 3PID.
+#   - two for ratelimiting how often invites can be sent in a room or to a
+#     specific user.
 #
 # The defaults are as shown below.
 #
@@ -862,6 +864,14 @@ log_config: "CONFDIR/SERVERNAME.log.config"
 #rc_3pid_validation:
 #  per_second: 0.003
 #  burst_count: 5
+#
+#rc_invites:
+#  per_room:
+#    per_second: 0.3
+#    burst_count: 10
+#  per_user:
+#    per_second: 0.003
+#    burst_count: 5
 
 # Ratelimiting settings for incoming federation
 #