Add a default worker concurrency for local dev (#2190)

Author: rhysyngsun

env/backend.env

@@ -1,6 +1,9 @@
 CELERY_BROKER_URL=redis://redis:6379/4
 CELERY_RESULT_BACKEND=redis://redis:6379/4
 CELERY_TASK_ALWAYS_EAGER=False
+# this should keep memory usage under the limit
+# if you need to increase this you also need to increase services.celery.mem_limit
+CELERY_WORKER_CONCURRENCY=8
 
 # local hostname shenanigans
 CORS_ALLOWED_ORIGINS='["http://open.odl.local:8062"]'