Add Perseus database type

[gabrieljackson]

This change includes the basic functionality needed to deploy the Perseus database proxy service and to use it for new installations.

High Level Perseus Architecture:

Reviewer Notes:

• Although this PR refactors some of the shared code with PGBouncer, there is a lot more we can do. Out of a desire to not break anything some code was duplicated for now with some minor tweaks which can be improved later.
• Some PGBouncer provisioning happens as part of Perseus database setup. This is intended to allow for migrations to and from PGBouncer in the future. It's easier to do this stuff proactively instead of needing to do extensive updates later.
• Sorry, I tried to keep this change smaller, but this is all needed for basic functionality.

Add Perseus database type

[fmartingr]

Following logic was a bit tricky at first but this looks good to me, my only worries are with naming (commented out below) on parts that I did not fully understand or found confusing. Some tests for the critical methods would also be nice.

Although this PR refactors some of the shared code with PGBouncer, there is a lot more we can do. Out of a desire to not break anything some code was duplicated for now with some minor tweaks which can be improved later.

Can you put comments on the ones you already duplicated so we can easily track those?