feat(persistence): create pgx store

[slonka]

⚠️ Please review with "w=1" - https://github.com/kumahq/kuma/pull/6359/files?w=1 to not show whitespace changes (I added Context() in tests and that added indent so without "w=1" it shows a lot of code that did not actually change).

There seems to be a weird behaviour in either pool.Close() / db.Close() or postgres itself that it does not always close the connections. As a workaround I'm bumping max_connections to 10k.

Side note:

• deterministically not closing connections:
  • Bart's amd64 VM and amd64 macbook
  • My and Marcin's arm64 macbook
• deterministically closing connections:
  • amd64 circleci VM

Closes #6363

Checklist prior to review

• Link to relevant issue as well as docs and UI issues --
• This will not break child repos: it doesn't hardcode values (.e.g "kumahq" as a image registry) and it will work on Windows, system specific functions like syscall.Mkfifo have equivalent implementation on the other OS --
• Tests (Unit test, E2E tests, manual test on universal and k8s) --
• Do you need to update UPGRADE.md? --
• Does it need to be backported according to the backporting policy? --
• Do you need to explicitly set a > Changelog: entry here or add a ci/ label to run fewer/more tests?

[lahabana]

Just nits