Allow Pushy Server to optionally use SSL for establishing database connections

[zanecodes]

Description

This change allows Pushy Server to be configured to use SSL to connect to the PostgreSQL database. This is necessary when using Azure Database for PostgreSQL as an external database securely, without disabling Enforce SSL. This change will not actually work until the pinned version of sqerl is bumped to at least https://github.com/chef/sqerl/commit/f36fb5c80777769ff9c27adba9340693cfe964f8, and https://github.com/chef/chef_secrets/pull/26 is merged and the dependency is updated here.

Issues Resolved

https://github.com/chef/chef-server/issues/1559

Check List

• [ ] New functionality includes tests
• [ ] All tests pass
• [x] All commits have been signed-off for the Developer Certificate of Origin. See https://github.com/chef/chef/blob/master/CONTRIBUTING.md#developer-certification-of-origin-dco