Add grafana-oncall-app.user-settings:read permission to notifications…

… receiver role (#4340)

# What this PR does
Adding `grafana-oncall-app.user-settings:read` Notifications Receiver so
that it can use `get_backend_verification_code`

## Which issue(s) this PR closes

Closes [issue link here]

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## Checklist

- [ ] 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

@@ -273,6 +273,7 @@
         "permissions": [
           { "action": "plugins.app:access", "scope": "plugins:id:grafana-oncall-app" },
           { "action": "grafana-oncall-app.notifications:read" },
+          { "action": "grafana-oncall-app.user-settings:read" },
           { "action": "grafana-oncall-app.user-settings:write" }
         ]
       },