Decomposed database (main + ci) should work with PgBouncer

We have reports of Omnibus not working when PgBouncer + decomposed (&7509 (comment 1209289798)) - this was with GET

We should validate that :

• Omnibus works out of the box with decomposed (main + ci) databases sharing a PostgreSQL instance, with PgBouncer in front.
• Fix any issues preventing this from working.

/cc @nwestbury @twk3 @WarheadsSE