Refactor MIC Client

[fredrikhr]

• Retire IMicClient interface
  there is only one implementation, and 3^rd parties can subclass the MicClient class instead.
• Make unit tests use secure files in Azure DevOps to perform actual MIC requests
• Re-create the MQTT sample application
• Make Unit Tests using HttpClientFactory and the .NET Core Generic Host
• Add missing APIs from the Cloud REST API
• GraphQL integration

Additional APIs

ref.: Telenor Connexion Managed IoT Cloud, version 2.50.0
Documentation: https://docs.telenorconnexion.com/mic

Cloud REST API

• Auth API complete
• User API complete
  Role endpoints not included due to documentation stating they are unstable and in development.