feat: add support for postgres ssl mode and root cert (#3182)

this PR adds support for configuring `sslmode` and `sslrootcert` when
initiating the psycopg2 connection.

closes #3181

llama_stack/providers/utils/kvstore/config.py

@@ -75,6 +75,8 @@ class PostgresKVStoreConfig(CommonConfig):
     db: str = "llamastack"
     user: str
     password: str | None = None
+    ssl_mode: str | None = None
+    ca_cert_path: str | None = None
     table_name: str = "llamastack_kvstore"
 
     @classmethod