[APPS-1355][WIP][PRI] Add an Oauth Sample App to demo apps

:koala: :construction: 

This PR intends to add a sample App that is dedicated to demonstrating to App developers how they can use OAuth in their App. Not our “ZAM” Oauth but the client side OAuth where every agent does oauth with the said service

### Screenshots

### Note

### Reference

* [JIRA](https://zendesk.atlassian.net/browse/APPS-1355)

/cc