Add `Sitegeist.Monocle:StaticUri` prototype

The prototype creates an URI that will return the content of the file and the contentType for the given key.

    endpointUrl = Sitegeist.Monocle:StaticUri {
        key = 'example'
    }

The path and content type for each key are configured via Settings:

Sitegeist:
  Monocle:
    uriMock:
      static:
        example:
          path: 'resource://Vendor.Package/Private/Json/example.json'
          contentType: 'application/json'