alertmanager: update to 0.25.0

prometheus/map.jinja

 {% set prometheus = salt['grains.filter_by']({
     'default': {
       'release': '2.42.0',
-      'alertmanager_release': '0.24.0',
+      'alertmanager_release': '0.25.0',
       'node_exporter_release': '1.5.0',
     }
 }, grain='os_family', merge=salt['pillar.get']('prometheus')) %}