Additional connector param required for Redshift

[SteveDMurphy]

Is your feature request related to a specific problem?

When using a bastion host, an invalid SSL cert blocks the connection. As we are already connecting via SSH, it might make sense to allow the ssl certificate to be preferred instead of required.

Describe the solution you'd like

Optionally set {"sslmode": "prefer"} for Redshift if connecting via an SSH tunnel

Describe alternatives you've considered, if any

Also requiring the SSL certificate to be set and valid

Additional context

This created some connection errors in production when testing with a bastion host.

I'm using this documentation as a basis for some of the thoughts behind this