make the job event bigint migration chunk size configurable

awx/main/tasks.py

@@ -692,7 +692,7 @@ def migrate_legacy_event_data(tblname):
     with advisory_lock(f'bigint_migration_{tblname}', wait=False) as acquired:
         if acquired is False:
             return
-        chunk = 1000000
+        chunk = settings.JOB_EVENT_MIGRATION_CHUNK_SIZE
 
         def _remaining():
             try:

awx/settings/defaults.py

@@ -197,6 +197,9 @@ JOB_EVENT_WORKERS = 4
 # The maximum size of the job event worker queue before requests are blocked
 JOB_EVENT_MAX_QUEUE_SIZE = 10000
 
+# The number of job events to migrate per-transaction when moving from int -> bigint
+JOB_EVENT_MIGRATION_CHUNK_SIZE = 1000000
+
 # Disallow sending session cookies over insecure connections
 SESSION_COOKIE_SECURE = True