Add Keycloak Device Authorization Grant Quickstart

[uzmamansoor09]

Description

Add a quickstart on how to use Keycloak's endpoints for input-constrained devices. Also add documentation

Discussion

No response

Motivation

Right now, the quickstarts focus on standard authorization flows. There is a lack of documentation for input-constrained devices.

Details

An example of what the quickstart would look like:
-> Device 1 -> Springboot application (using keycloak's device authorization grant flow) -> add frontend
-> Connection to device 2 would be tested with curl commands in README

[msdaly200]

You might want to create some subtasks for each part of this:

1. Admin console config - exported to realm-export.json file
2. Device 1 e.g. smart TV - app1 - configured to send POST requests, display user_code/QR Code, and app probably needs to poll for when the second device connects.
3. Device 2 e.g. phone - app2 - have uri that can be visited and user log in with consent screen - "Do you want to grant 'Smart TV App' access to your account?"
4. Testing
5. Documentation/Readme.md.