Load TLS certificates from Traefik

FlowGuard can now load certificates from a Traefik v2 or v3 acme.json file. Enter its path in a proxy's Advanced settings, or let flowguard setup discover it, to use certificates already managed by Traefik. The proxy watches the file for renewals.

Requires FlowGuard Proxy v0.16.0 or newer and access to the acme.json file.