Add existing docker container to Caprover

Is your feature request related to a problem? Please describe. I have some applications that are way easyer to maintain outside caprover using docker-compose. However it is trick to register them with the caprover nginx as proxy.

Describe the solution you'd like Add existing container to caprover in a read-only mode (no write access to env-variables, volumes ...). Allow to configure the http port and assign domain names. Also use certbot.