Feature request: support `sslpassphrase` parameter in connection string parsing

Describe the solution you'd like

Parse the sslpassphrase query parameter and assign it to config.ssl.passphrase, similar to how other SSL-related parameters are handled.

Example

Given the following connection string: postgres://user:pass@host:5432/db?sslmode=verify-full&sslrootcert=/path/to/ca.crt&sslcert=/path/to/client.crt&sslkey=/path/to/client.key&sslpassphrase=MySecretPass

I'd be happy to submit a PR for this.