Add PostgreSQL support

[MlrdTebr]

Currently VotingPlugin only supports the existing database backends (e.g., MySQL / SQLite — whatever is currently supported). Many server operators and host providers standardize on PostgreSQL, and some managed hosting platforms provide PostgreSQL as the preferred or only relational DB. Without PostgreSQL support, users who rely on PostgreSQL must run an extra database service or convert data, reducing adoption and making maintenance harder. I'm frequently frustrated when a plugin I want to use has no PostgreSQL option and I need to provision another DB. (Also PostgreSQL a little bit more performance)

Add PostgreSQL support as an optional, configurable database backend for VotingPlugin.

[BenCodez]

After looking into it for a few minutes it doesn't appear to be too complicated to add, I'll try to add it here shortly

[BenCodez]

https://bencodez.com/job/VotingPlugin/

403579d

Haven't tested PostgreSQL yet, but I think it should work, let me know if it doesn't