Elaborate more about the manifest settings for "datastores-access"

[airpingu]

For example, the data store won't be read-only to the Messaging App which can claim the following entry in its manifest:

{
  datastores-access: {
    "messaging": {
      "access": "readwrite",
      "description": "access the messaging stores"
    }
  }
}

For other apps that just want to read the data store, it can simply claim:

{
  datastores-access: {
    "messaging": {
      "access": "readonly",
      "description": "access the messaging stores"
    }
  }
}

If the app doesn't claim the datastores-access entry in its manifest, the getDataStores("messaging") will return nothing to it, which means it can neither read or write the data stores.

[zolkis]

More exactly, the Promise resolves to an error.

[airpingu]

Solved this at https://github.com/airpingu/data-store-api/commit/1d61dce41152404ae327013ec7d3cbf88190b3ff.