Ensure compose deployments have configurable domain names on prod

[spwoodcock]

Is your feature request related to a problem? Please describe.

• Prior to Replace custom nginx / certbot config with BunkerWeb #1695 we had an easily configurable Nginx server with domain names injected at runtime.
• After integrating BunkerWeb (for many reasons described in the PR), the domain name configuration is based on environment variable names, which cannot be dynamic in a compose.yaml.
  • For now, the domains are hardcoded for the HOTOSM domains.
• Instead we will need to manually convert variable placeholders to their required values in dev/stage/prod.

Describe the solution you'd like

• Using envsubst, we should add a stage where the compose files are processed first, with domains injected in.
• Sometimes there are double nested variables, so we will need to run multiple times.
• source .env --> envsubst -i in.yaml -o out.yaml --> docker compose ...

Describe alternatives you've considered

• Another WAF without these requirements, but our selection process is described in https://github.com/hotosm/fmtm/blob/development/docs/decisions/0006-web-app-firewall.md