feat: Adds monitoring setup for prometheus push gateway

.env.sample

@@ -9,10 +9,16 @@ RESTIC_REPOSITORY=/backups/restic
 CRON_SCHEDULE='30 3 * * *'
 
 # Push Notifiactions
+#PUSH_PROMETHEUS_URL=https://pushgateway.example.com/metrics/job/backup
+# or
 #PUSH_URL_START=https://status.example.com/api/push/xxxxxxxxxx?status=up&msg=start
 #PUSH_URL_SUCCESS=https://status.example.com/api/push/xxxxxxxxxx?status=up&msg=OK
 #PUSH_URL_FAIL=https://status.example.com/api/push/xxxxxxxxxx?status=down&msg=fail
 
+# Push Basic Auth
+#COMPOSE_FILE="$COMPOSE_FILE:compose.pushbasicauth.yml"
+#SECRET_PUSH_BASICAUTH=v1
+
 # swarm-cronjob, instead of built-in cron
 #COMPOSE_FILE="$COMPOSE_FILE:compose.swarm-cronjob.yml"