[v9.3.x] Add object_matchers example (#61558)

Add object_matchers example (#61235)

* Add object_matchers example

* Use better terminology

(cherry picked from commit 3db08d4e36)

Co-authored-by: Alex Moreno <alexander.moreno@grafana.com>

docs/sources/alerting/set-up/provision-alerting-resources/file-provisioning/index.md

@@ -516,9 +516,16 @@ policies:
     #        a very low alert volume or your upstream notification system performs
     #        its own grouping.
     group_by: ['...']
-    # <list> a list of matchers that an alert has to fulfill to match the node
+    # <list> a list of prometheus-like matchers that an alert rule has to fulfill to match the node (allowed chars
+    #        [a-zA-Z_:])
     matchers:
       - alertname = Watchdog
+      - service_id_X = serviceX
+      - severity =~ "warning|critical"
+    # <list> a list of grafana-like matchers that an alert rule has to fulfill to match the node
+    object_matchers:
+      - alertname = CPUUsage
+      - service_id-X = serviceX
       - severity =~ "warning|critical"
     # <list> Times when the route should be muted. These must match the name of a
     #        mute time interval.