adding functionality for azure default, and managed identity login

[svenkerud]

Hi, As mentioned in the Issue report #21, we had a use-case where we wanted to use this tap, but wanted to avoid the use of service principals if possible.

This PR includes our proposed changes to the Authenticator property of the RESTStream -> MMSGraphStream.
We have added the property managed_identity to the config, and set client_id and client_secret to required=False to support additional authentication methods. tenant remains required.

The logic now is such:

1. if client_id and client_secret are set use the original authentication method, thus maintaining backwards compatibility.
2. if managed_identity is set, it will use Azure.ManagedIdentityCredentials
3. if neither: client_id ,client_secret or managed_identity are set it will use Azure.DefaultCredentials.

We hope you will accept these changes. Tests to confirm the behaviour ar included.
Let us know if there is anything you want us to adjust.