Adding support for SSL and connection string for Postgres client + SSL tests (2nd commit)

[jackyalbo]

Explain the changes

1. Adding support for SSL/TLS for working with an external Postgres DB. in case of adding env variable POSTGRES_SSL_REQUIRED
2. Adding support for supporting self-signed server certificate, by using env variable POSTGRES_SSL_UNAUTHORIZED
3. Adding support to work with client certificate - when located in /etc/external-db-secret (like for MGMT and S3)
4. Adding support to work with a unified connection string (instead of providing host, dbname, port, and creds) with POSTGRES_CONNETION_STRING env variable

Testing:
5. Added docker builder to create an SSL-supported version for external PG (v15)
6. Added Makefile actions for building this docker image: build_ssl_postgres
7. Added Makefile for running sanity and unit test on top of the docker image for SSL Postgres
8. Added actions to run both sanity and unit test for SSL Postgres

Issues: Fixed #xxx / Gap #xxx

Testing Instructions:

• Doc added/updated
• Tests added