Update UI plugin to be define how Gateway Service can serve static files as plugin

[andrei2699]

When we bundle the UI plugin along with the other code, we could serve the static files if any instead of having a dedicated server run

The UI plugin manifest should be updated to notify the Gateway Service that we should serve the file. Internally the Gateway Service should expose the remoteEntry.js(json) as it being from the url itself, as part of the application