Draft: POC Add doorkeeper device auth support

What does this MR do and why?

Adds support for OAuth2 device grant flow

This adds support for OAuth device authorization grant using the doorkeeper_device_authorization_grant gem.

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Before	After

How to set up and validate locally

1. Create a non-confidential OAuth2 application. Make a note of the client ID generated for step 2.

2. Run the following command to get a device code and authorization URL

   curl -X POST \
       -H "Content-Type: application/x-www-form-urlencoded" \
       -d 'client_id=<applicationid/clientid from Step 1>&scope=api' \
       http://localhost:3000/oauth/authorize_device

3. You will receive a response such as the following:

{
    "device_code":"abcd",
    "user_code":"NHJ1YLTF",
    "verification_uri":"http://localhost:3000/oauth/device",
    "verification_uri_complete":"http://localhost:3000/oauth/device?user_code=NHJ1YLTF",
    "expires_in":300,
    "interval":5
}

Make a note of the Device Code and Verification URL complete for the next step.

4. Open up the verification URL and click on Authorize
5. Make another curl request to fetch the access_token

curl -X POST \
    -H "Content-Type: application/x-www-form-urlencoded" \
    -d 'client_id=<client id from step 1>&grant_type=urn:ietf:params:oauth:grant-type:device_code&device_code=<device code from step 3>' \
    http://localhost:3000/oauth/token