GF_SERVER_DOMAIN expects a bare hostname (e.g. grafana.example.com) but
was set to SERVICE_URL_GRAFANA which includes the protocol
(https://grafana.example.com). This mismatch can cause Grafana to fail
to load its application files when deployed behind Coolify's proxy.
Changed to SERVICE_FQDN_GRAFANA which provides just the hostname. Applied
the fix to both grafana.yaml and grafana-with-postgresql.yaml templates.
Fixes#5307
