contrib: add a new postgres inspector filter

[agrawroh]

Description

We have a few use-cases where we'd like to inspect the SNI of the incoming Postgres connections and then based on the SNI go connect to the Database. This is not possible today.

This PR adds a new Postgres Inspector filter in Contrib which could be used to populate the protocol as "postgres" and be chained with TLS Inspector to extract the SNI. SNI could later be used in TCP Proxy to connect to a unique Database.

---

Commit Message: contrib: add a new postgres inspector filter
Additional Description: Added a new Contrib filter for Postgres Inspector which would be responsible for inspecting the incoming TLS PG connections.
Risk Level: Low
Testing: Added Unit & Integration Tests
Docs Changes: Added
Release Notes: Added

[repokitteh-read-only]

As a reminder, PRs marked as draft will not be automatically assigned reviewers,
or be handled by maintainer-oncall triage.

Please mark your PR as ready when you want it to be reviewed!

🐱

Caused by: #40803 was opened by agrawroh.

see: more, trace.

[agrawroh]

/retest

[ravenblackx]

Adding me as the maintainer to stop the on-call thing from nagging, but I'm just here to stamp it after it passes other reviews since it's contrib. Ping me on slack when it's ready for that.

[ravenblackx]

1. Adding the waiting tag which usually means it's the author's turn, but here means only "the envoy maintainer nag isn't useful because the PR is waiting for the other reviewer".