Add pg_sslmode parameter description (#153)

* Add `pg_sslmode` parameter description

* Update index.md

* Update index.md

Author: ewgenius

spiceaidocs/docs/data-connectors/postgres/index.md

@@ -24,6 +24,10 @@ The connection to PostgreSQL can be configured by providing the following `param
 - `pg_user`: The username to connect with.
 - `pg_pass_key`: The secret key containing the password to connect with.
 - `pg_pass`: The raw password to connect with, ignored if `pg_pass_key` is provided.
+- `pg_sslmode`: Optional parameter, specifies the SSL/TLS behavior for the connection, supported values:
+  - `prefer`: (default) This mode will try to establish a secure SSL connection if possible, but will connect insecurely if the server does not support SSL.
+  - `required`: This mode requires an SSL connection. If a secure connection cannot be established, server will not connect.
+  - `disable`: This mode will not attempt to use an SSL connection, even if the server supports it.
 
 Configuration `params` are provided either in the top level `dataset` for a dataset source and federated SQL query, or in the `acceleration` section for a data store.