Create an approved site when using device code flow

[federicaagostini]

The device code flow did not imply the creation of an approved site when the user give the consent to the client, as the authorization code flow does. This PR adds an approved site using the same logic as the authorization code flow. Moreover, when the user approves a client with name prefix oidc-agent:, the client will be automatically linked to the user. Lastly, the scope policy filter has been added here for both the authorization code flow and device code flow.

This required to move (and cleanup) MitreID classes related to the device code flow into IAM.