fix: better grouping for template

Co-authored-by: v-zhuravlev <[email protected]>

traefik-mixin/alerts/alerts.libsonnet

@@ -16,8 +16,8 @@
             annotations: {
               summary: 'Traefik is failing to reload its configuration.',
               description: |||
-                Traefik is failing to reload its config in {{ $labels.environment }}.
-              |||,
+                Traefik is failing to reload its config in {{ $labels.%(firstGroupLabel)s }}.
+              ||| % {firstGroupLabel: std.split($._config.groupLabels, ',')[0]},
             } + std.get($._config, 'alertAnnotations', {}),
           },
           {