Support custom ssl certificates for all services

[benniekiss]

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

Netbird allows setting up ssl certificates via certbot/letsencrypt, but only the management service allows passing a custom pre-generated cert via a commandline flag. The signal service allows passing an ssl directory, but not the specific files. And the dashboard interface is not configurable with a custom certificate. These disparate methods make self hosting with https support complicated and confusing.

Describe the solution you'd like

Allow passing an --ssl-cert and --ssl-key param to all services, and a NETBIRD_SSL_CERT and NETBIRD_SSL_KEY env var to all containers. These would accept a path to a custom ssl certificate and key.

Describe alternatives you've considered

Manually configure each service with a custom certificate, which for the dashboard would involve hacking around the nginx config.

Additional context