Add option for custom ACME CA

Is your feature request related to a problem? Please describe.
I would like this tool to be used with a self signed CA in an internal environment that has an acme compliant server. I'm currently using Step CA for my acme compliant server. I currently don't have the option to use my own acme server without a ton of involved reconfiguration.

Describe the solution you'd like
An advanced configuration option where you can upload a self signed CA and give a custom acme compliant url to be used with a given host.

Describe alternatives you've considered
I am currently using a combination of jwilder/nginx-proxy and the encrypt companion to accomplish the same task with a custom acme CA, but it would be ideal to have a graphical frontend for a reverse proxy that can pull a valid internal cert, route traffic to separate physical hosts as needed and also the underlying containers running on the same machine.

Additional context

No files, tests, or entry points are named in the issue. Start by tracing how per-host ACME settings and certificate authorities are currently configured, then define the scope for uploading a self-signed CA and supplying a custom ACME-compliant URL; done means both can be configured for a host and used to obtain its certificate.