Increase rc_invites.per_issuer for Complement (#18072)

It's possible to run into `SynapseError: 429 - Too Many Requests (rc_invites.per_issuer)`

`rc_invites.per_issuer` originally introduced in
https://github.com/matrix-org/synapse/pull/13125

docker/complement/conf/workers-shared-extra.yaml.j2

@@ -85,6 +85,9 @@ rc_invites:
   per_user:
     per_second: 1000
     burst_count: 1000
+  per_issuer:
+    per_second: 1000
+    burst_count: 1000
 
 federation_rr_transactions_per_room_per_second: 9999