FR: Image with no postgres, or ability to disable postgres

[jerrywoo96]

Hello,

Thanks for maintaining this project. I would like to request for an image that does not require postgres db, as i am the only sole user of this application. I would like to configure the authentication and the list of connection endpoints through the user-mapping.xml file as documented at https://guacamole.apache.org/doc/gug/configuring-guacamole.html

Thank you!