Enable use of Amazon RDS CA certificate in driver

Currently, the standard Amazon RDS CA root certificate is not being bunded with the ODBC driver.

[Download an SSL certificate for your managed database in Amazon Lightsail | Lightsail Documentation](https://lightsail.aws.amazon.com/ls/docs/en_us/articles/amazon-lightsail-download-ssl-certificate-for-managed-database)

https://s3.amazonaws.com/rds-downloads/rds-ca-2019-root.pem

An attempt was made to enable this in the driver, without success.

`tls_options.ca_file("path-to-file")`

However, this did not seem to work as expected.

So currently, we are allowing invalid server certificates

`tls_options.allow_invalid_certificates(true)`

This task is to resolve the issue of using a CA file, distribute the CA certificate and re-enable server certificate checking.

The issue names tls_options.ca_file and tls_options.allow_invalid_certificates; start by tracing those entry points through the driver and its TLS setup. Done means CA-file loading works, the RDS CA certificate is distributed, and server-certificate checking is enabled against a managed database connection.

Written by the indexing model from the issue text.