Set signal flags from environment variables

[Silex]

Describe your changes

Hello, I like the idea of being able to configure the services from an env file for the relay service (e.g NB_LISTEN_PORT), so I copied this to the relay service.

I did not test nor compile the code, just did what looked correct.

If it happens to be correct, I'll also do it with the other services (management).

Once merged, we should be able to go from:

  signal:
    image: netbirdio/signal:$NETBIRD_SIGNAL_TAG
    command: ["--letsencrypt-domain", "foo.com", "--ssl-dir", "/etc/letsencrypt"]

To:

  signal:
    image: netbirdio/signal:$NETBIRD_SIGNAL_TAG
    environment:
      NB_LETSENCRYPT_DOMAIN: foo.com
      NB_SSL_DIR: /etc/letsencrypt

Or better use an env_file and have better agnosticism in the docker-compose file.

Issue ticket number and link

Stack

Checklist

• [ ] Is it a bug fix
• [ ] Is a typo/documentation fix
• [x] Is a feature enhancement
• [ ] It is a refactor
• [ ] Created tests that fail without the change (if possible)
• [ ] Extended the README / documentation, if necessary

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