Add PostgreSQL SSL connection options, resolves #16

[dhirajsb]

Description

Added CR properties to configure cert, key, key password, and CA certs for PostgreSQL SSL connection.
Resolves #16

How Has This Been Tested?

Tested configuration manually by creating secrets and setting the SSL properties manually.
However, mlmd Docker image has an issue with creating a PostgreSQL SSL connection,
See: google/ml-metadata#187

Merge criteria:

• The commits and have meaningful messages; the author will squash them after approval or will ask to merge with squash.
• Testing instructions have been added in the PR body (for PRs involving changes that are not immediately obvious).
• The developer has manually tested the changes and verified that the changes work

[tarilabs]

I understand this enables custom certs for ssl connection to Postgresql.

Thank you!

[tarilabs]

If sslMode=required is not working, would it make sense to not have it in our options (adding comment to upstream https://github.com/google/ml-metadata/issues/187#issue-2005410819 issue?)

I understand that is orthogonal to this PR scope, just noticed thought about mentioning