feat: add a new test that produces stored notifs

[pjenvey]

(a quick, initial implementation)

this uses the more basic websocket.WebSocket as WebSocketApp.run_forever
doesn't seem to handle the workflow needed (where the websocket is kept
disconnected for a large portion of the test)

Issue: SYNC-3916

[pjenvey]

What's changed between this and locustfile.py:

4694798...feat/stored-notifs-SYNC-3916

[jrconlin]

Do we want to include the enableTrace and setdefaulttimeout that were defined in locustfile.py?

[pjenvey]

Nope because it's global it should only be done in one place, especially since we invoke locust on both locustfile/stored.py. Those lines should probably move out of locustfile.py into a shared module eventually.

[Trinaa]

Are you wanting to update the load.py Shape to include a percentage of this type of user? Or maybe this is a follow-up?

Also I'm curious if the on_ws lifecycle methods are working?

[jrconlin]

Aaand looks like black became more pedantic about the comment strings.

[pjenvey]

Are you wanting to update the load.py Shape to include a percentage of this type of user? Or maybe this is a follow-up?

Let's make this a followup, we'll probably initially start with solely using StoredAutopushUser by itself.

Also I'm curious if the on_ws lifecycle methods are working?

Only on_ws_message is used here -- the others should be removed from this module later when we clean this up further.