appliance/postgresql: Raise pg `max_connections` to 400
appliance/postgresql: Raise pg `max_connections` to 400

Signed-off-by: Kyle Brett <3c25b01657254677d3e1a8fd1f0742c5d489bd39@kylebrett.com>

philiplb/flynn,flynn/flynn,flynn/flynn,philiplb/flynn,philiplb/flynn,flynn/flynn,benbjohnson/flynn,benbjohnson/flynn,philiplb/flynn,lmars/flynn,lmars/flynn,flynn/flynn,benbjohnson/flynn,philiplb/flynn,flynn/flynn,benbjohnson/flynn,lmars/flynn,lmars/flynn,benbjohnson/flynn,lmars/flynn,benbjohnson/flynn