feat(connections): add UI for PostgreSQL SSL client certificates (sslcert, sslkey, sslrootcert)

[ZhuchkaTriplesix]

PostgreSQL connections support TLS only via raw URI parameters (sslcert=, sslkey=, sslrootcert=). There is no file picker or input fields in the connection form for client certificates or custom CA roots.

Impact: Users connecting to managed/cloud Postgres with strict TLS (e.g. corporate CA, mTLS) must hand-craft URIs and ensure certificate paths are correct on every machine.

Expected: Provide UI fields or file pickers for sslrootcert, sslcert, and sslkey, and build the URI from them.

Acceptance criteria:

• Add optional certificate/CA inputs to the PostgreSQL form.
• Store certificate paths in the connection row or secure store.
• Include them in the generated URI or driver SecurityContext.