AddHandler / RemoveHandler are not thread-safe

## Description of the new feature

AzureSession.Instance.ClientFactory.AddHandler and AzureSession.Instance.ClientFactory.RemoveHandler are used by service client to add additional handler into HTTP pipeline. But handlers will be shared across services. When service only wants to register dedicated handler and remove it after cmdlet execution, there is thread-safe problem because registered handlers will be shared with other service client. We need a new design to mitigate this problem.

## Proposed implementation details (optional)

Start by tracing AzureSession.Instance.ClientFactory.AddHandler and RemoveHandler and how service clients use the HTTP pipeline. Define a design that prevents handlers registered for one service or cmdlet execution from being shared or modified concurrently by other service clients; done means concurrent client use is thread-safe.

Written by the indexing model from the issue text.