Celery tuning (#17262)

* Celery tuning

Primarily focused on being able to explicitly set `--concurrency` in prod.

Unfortunately Celery doesn't respect an environment variable for this, so allow for setting additional Celery flags via the environment.

Also sets the dev worker to a concurrency of 1 to fix a locking issue with running Beat in the same process leading to many tasks being enqueued instead of one.

* specifically limit to --concurrency

Procfile

@@ -2,7 +2,7 @@ release: bin/release
 web: bin/start-web ddtrace-run python -m gunicorn.app.wsgiapp -c gunicorn-prod.conf.py warehouse.wsgi:application
 web-api: bin/start-web ddtrace-run python -m gunicorn.app.wsgiapp -c gunicorn-prod.conf.py warehouse.wsgi:application
 web-uploads: bin/start-web ddtrace-run python -m gunicorn.app.wsgiapp -c gunicorn-uploads.conf.py warehouse.wsgi:application
-worker: bin/start-worker celery -A warehouse worker -Q default -l info --max-tasks-per-child 32
+worker: bin/start-worker celery -A warehouse worker --concurrency=${CELERY_CONCURRENCY:-1} -Q default -l info --max-tasks-per-child 1024
 worker-beat: bin/start-worker celery -A warehouse beat -S redbeat.RedBeatScheduler -l info
-worker-traced: env DD_SERVICE=warehouse-worker bin/start-worker ddtrace-run celery -A warehouse worker -Q default -l info --max-tasks-per-child 32
-worker-drain-sqs: env BROKER_URL=sqs:///?region=us-east-2&queue_name_prefix=pypi-worker bin/start-worker celery -A warehouse worker -Q default -l info --max-tasks-per-child 32
+worker-traced: env DD_SERVICE=warehouse-worker bin/start-worker ddtrace-run celery -A warehouse worker --concurrency=${CELERY_CONCURRENCY:-1} -Q default -l info --max-tasks-per-child 32
+worker-drain-sqs: env BROKER_URL=sqs:///?region=us-east-2&queue_name_prefix=pypi-worker bin/start-worker --concurrency=${CELERY_CONCURRENCY:-1} celery -A warehouse worker -Q default -l info --max-tasks-per-child 1024

docker-compose.yml

@@ -160,7 +160,7 @@ services:
   worker:
     image: warehouse:docker-compose
     pull_policy: never
-    command: hupper --shutdown-interval 10 --reload-interval 10 -m celery -A warehouse worker --beat --scheduler redbeat.RedBeatScheduler -l info
+    command: hupper --shutdown-interval 10 --reload-interval 10 -m celery -A warehouse worker --concurrency=1 --beat --scheduler redbeat.RedBeatScheduler -l info
     volumes:
       - ./warehouse:/opt/warehouse/src/warehouse:z
       - packages:/var/opt/warehouse/packages