Undo adding new API to IAzureContextContainer

[isra-fel]

Adding APIs to well-known types (IAzureContextContainer in this case) is risky as:

• It is a binary breaking change - what if someone implements the interface in their own code
• It is harder not to introduce breaking change the bigger the interface grows.

So, we came up with a pattern to avoid touching IAzureContextContainer, using ComponentRegistery.
Related powershell PR: Azure/azure-powershell#15743