[RH-SSO 7.6.X container images] Explore the possibility to make the SSL "sso76-x509-postgresql-persistent" template self-containing / self-defining (usable in offline mode too)

See SSOSUP-337 for original issue report. The issue summary in short being as follows:

While the current implementation of the SSL sso76-x509-postgresql-persistent template follows the instructions of the PostgreSQL image on how to configure/enable the SSL/TLS support:

• https://catalog.redhat.com/software/containers/rhel8/postgresql-13/5ffdbdef73a65398111b8362
• https://github.com/sclorg/postgresql-container/tree/master/examples/enable-ssl

the current form of the template isn't self-containing/self-defining in the sense access to external repository is necessary to be able to perform S2I extending the default PostgreSQL image to add SSL/TLS support. Therefore, the current implementation can't be out-of-the-box used in disconnected installations, where just the template file is downloaded.

Explore the possibility if it would be possible to replace external access to .s2i directory with static information/static objects (e.g. hopefully via some way via a Dockerfile build), which would remove the need this template to have network access.