persistent-postgresql: add `createPostgresqlPoolTailored` function

[ixmatus]

This change adds a connection pool creation function that is just like the createPostgresqlPoolModifiedWithVersion function but that can take a custom open'-like connection-creation function.

The motivation for this change is that we need to be able to customize the resource creation action dynamically at run-time.

Before submitting your PR, check that you've:

• [X] Documented new APIs with Haddock markup
• [X] Added @since declarations to the Haddock
• [X] Ran stylish-haskell on any changed files.
• [X] Adhered to the code style (see the .editorconfig file for details)

After submitting your PR:

• [x] Update the Changelog.md file with a link to your PR
• [X] Bumped the version number if there isn't an (unreleased) on the Changelog
• [ ] Check that CI passes (or if it fails, for reasons unrelated to your change, like CI timeouts)

[parsonsmatt]

Can you repush to trigger CI? Not sure why it isn't going

[ixmatus]

@parsonsmatt I just re-pushed but that looks like it didn't trigger CI.

[parsonsmatt]

Sorry for the delay - released as persistent-postgresql-2.13.6