jvb: add fallback WS server ID

When XMPP is not used there is no value set.

jvb/rootfs/defaults/jvb.conf

@@ -21,7 +21,7 @@
 {{ $PUBLIC_URL_DOMAIN := .Env.PUBLIC_URL | default "https://localhost:8443" | trimPrefix "https://" | trimSuffix "/" -}}
 {{ $SHUTDOWN_REST_ENABLED := .Env.SHUTDOWN_REST_ENABLED | default "false" | toBool -}}
 {{ $WS_DOMAIN := .Env.JVB_WS_DOMAIN | default $PUBLIC_URL_DOMAIN -}}
-{{ $WS_SERVER_ID := .Env.JVB_WS_SERVER_ID | default .Env.JVB_WS_SERVER_ID_FALLBACK -}}
+{{ $WS_SERVER_ID := .Env.JVB_WS_SERVER_ID | default .Env.JVB_WS_SERVER_ID_FALLBACK | default "default" -}}
 {{ $WS_TLS := .Env.JVB_WS_TLS | default "1" | toBool -}}
 {{ $XMPP_AUTH_DOMAIN := .Env.XMPP_AUTH_DOMAIN | default "auth.meet.jitsi" -}}
 {{ $XMPP_INTERNAL_MUC_DOMAIN := .Env.XMPP_INTERNAL_MUC_DOMAIN | default "internal-muc.meet.jitsi" -}}