Support env replacement in hop proxy

[Jasonej]

This loads in the .env from where hop proxy is run if it exists. This allows leveraging .env files to do things like make an env to control your desired proxy URL in a single spot.

.env

LOCAL_HOST=projectname.docker
PROXY_HOST=someproxy.example.com

docker-compose.override.yml

services:
  xxx-code:
    environment:
      - APP_URL=http${PROXY_HOST:+s}://${PROXY_HOST:-$LOCAL_HOST}
  xxx-web:
    environment:
      - VIRTUAL_HOST="${LOCAL_HOST},${PROXY_HOST:-}"

[Copilot]

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.