Depend on operator’s `release-0.30` branch

Note that, in effect, this also leads to kube-prometheus using
the latest patch-release of prometheus-operator, 0.30.1.

jsonnet/kube-prometheus/jsonnetfile.json

@@ -38,7 +38,7 @@
                     "subdir": "jsonnet/prometheus-operator"
                 }
             },
-            "version": "v0.30.0"
+            "version": "release-0.30"
         },
         {
             "name": "etcd-mixin",

jsonnetfile.lock.json

@@ -68,7 +68,7 @@
                     "subdir": "jsonnet/prometheus-operator"
                 }
             },
-            "version": "1b202471cb9847282198ec008b58bd7c34d9d2ff"
+            "version": "18fbf558ab7f8809fd610a3dc50bf483508dc1bb"
         },
         {
             "name": "etcd-mixin",

manifests/alertmanager-secret.yaml

 apiVersion: v1
 data:
-  alertmanager.yaml: Imdsb2JhbCI6IAogICJyZXNvbHZlX3RpbWVvdXQiOiAiNW0iCiJyZWNlaXZlcnMiOiAKLSAibmFtZSI6ICJudWxsIgoicm91dGUiOiAKICAiZ3JvdXBfYnkiOiAKICAtICJqb2IiCiAgImdyb3VwX2ludGVydmFsIjogIjVtIgogICJncm91cF93YWl0IjogIjMwcyIKICAicmVjZWl2ZXIiOiAibnVsbCIKICAicmVwZWF0X2ludGVydmFsIjogIjEyaCIKICAicm91dGVzIjogCiAgLSAibWF0Y2giOiAKICAgICAgImFsZXJ0bmFtZSI6ICJXYXRjaGRvZyIKICAgICJyZWNlaXZlciI6ICJudWxsIg==
+  alertmanager.yaml: Imdsb2JhbCI6CiAgInJlc29sdmVfdGltZW91dCI6ICI1bSIKInJlY2VpdmVycyI6Ci0gIm5hbWUiOiAibnVsbCIKInJvdXRlIjoKICAiZ3JvdXBfYnkiOgogIC0gImpvYiIKICAiZ3JvdXBfaW50ZXJ2YWwiOiAiNW0iCiAgImdyb3VwX3dhaXQiOiAiMzBzIgogICJyZWNlaXZlciI6ICJudWxsIgogICJyZXBlYXRfaW50ZXJ2YWwiOiAiMTJoIgogICJyb3V0ZXMiOgogIC0gIm1hdGNoIjoKICAgICAgImFsZXJ0bmFtZSI6ICJXYXRjaGRvZyIKICAgICJyZWNlaXZlciI6ICJudWxsIg==
 kind: Secret
 metadata:
   name: alertmanager-main