WIP: track whether MAUs are trial or not

...and only promote them to non-trial if we have MAU headroom

synapse/storage/schema/delta/52/free_mau.sql

@@ -14,5 +14,6 @@
  */
 
 ALTER TABLE monthly_active_users ADD COLUMN first_active BIGINT DEFAULT 0 NOT NULL;
+ALTER TABLE monthly_active_users ADD COLUMN trial BOOLEAN NOT NULL;
 
 CREATE INDEX monthly_active_users_first_active ON monthly_active_users(first_active);