[Feature Request] Support for DASH_HOST / DASH_PORT as environment overrides #3400

Is your feature request related to a problem? Please describe.
I'd like to be able to set DASH_HOST/DASH_PORT as environment variables to exclusively control the listen address for the dash server. HOST/PORT are too generic and collide with other services running on the same environment.

Describe the solution you'd like
Support DASH_HOST and DASH_PORT in addition to HOST and PORT, preferring DASH_HOST/DASH_PORT if they're provided.

Describe alternatives you've considered
I don't see any.

Additional context
From looking at #1134 it seems like the intention was to name this environment variable DASH_HOST, but for some reason it was implemented as just HOST. Not sure if this was a mistake but we probably can't remove support for HOST without a breaking change.