Add unit tests to verify enrollment authorization check during put and get operation in at_client

[sitaram-kalluri]

Is your feature request related to a problem? Please describe.

When an atSign undergoes authentication via the APKAM, the system verifies the key's namespace to ensure it's authorized for enrollment during both "put" and "get" operations. In the process of enrollment authorization check the following key-types are excluded : Reserved Keys, cached shared key and cached public key.

Currently there no unit tests in place to validate this behavior.

Describe the solution you'd like

Add unit tests to assert the enrollment authorization changes and the mentioned key types should be excluded from the enrollment authorization check.