Postgres connection pooling

[katajakasa]

Currently we have no limit in connection count, and if we run in ASGI mode, we can overflow postgres server connection limit -> 503 responses for everything.

Find ASGI compatible postgres pool for django, OR use postgres-drivers own, OR use some external pooling server.

[katajakasa]

Looks like this got done by django @ django/django@fad334e

Now we just wait for the next version.