Add missing permission to call machine learning plugin (#4983)

# What this PR does
- Permission necessary for OnCall to make webhook call to Machine
Learning was missing, this PR adds it.

## Which issue(s) this PR closes

Related to [issue link here]

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## Checklist

- [x] Unit, integration, and e2e (if applicable) tests updated
- [x] Documentation added (or `pr:no public docs` PR label added if not
required)
- [x] Added the relevant release notes label (see labels prefixed w/
`release:`). These labels dictate how your PR will
    show up in the autogenerated release notes.

grafana-plugin/src/plugin.json

@@ -616,6 +616,10 @@
         "action": "plugins.app:access",
         "scope": "plugins:id:grafana-labels-app"
       },
+      {
+        "action": "plugins.app:access",
+        "scope": "plugins:id:grafana-ml-app"
+      },
       {
         "action": "plugins:write",
         "scope": "plugins:id:grafana-oncall-app"