#7582799 Fix the Google Docs connection

This PR adds a description, example and Google Drive icon to the Google Drive connection manager setting.
It also fixes the Google Docs connection by handling it as a Calypso service in the same way Google Photos works.
The Google Drive connection is protected by a feature flag “google-drive” in config/development.json

Test

• Change to the fix/google_docs_connection branch.
• Go to http://calypso.localhost:3000/marketing/connections and pick a blog
• Note that the Google Drive connection now has an icon and description.
• Connect to your Google Account by clicking the “Connect” button. You may have problems in Firefox if you are using separate containers for Google and your development tab. Make sure they’re using the same container profile.
• When connected, the button will show “Disconnect”.

Before:

After:

Pre-merge Checklist

• Have you written new tests for your changes?
• Have you checked for TypeScript, React or other console errors?
• Have we added the “[Status] String Freeze” label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?