Right now, if add-credential is provided, we hard code BearerTokenCredentialPolicy:

We want to be able to generate another type of credentials, like AzureKeyCredentialPolicy
https://github.com/Azure/azure-sdk-for-python/blob/fffaf8226585b099a3b515e3cbd43acd9d59033d/sdk/core/azure-core/azure/core/pipeline/policies/_authentication.py#L97-L116

We want to add a --credential-type, by default the value is BearerTokenCredentialPolicy (backward compatible), but we could do --credential-type=AzureKeyCredentialPolicy.

We shall not be opinionated on checking if the string is known or not, let's assume whatever string is passed will be importable from azure.core.pipeline.policies