Logic Apps Extension Customization Features

[mathewc]

For Azure/azure-functions-host#9240 we did work to enable the Logic Apps team to implement a Dynamic Listeners feature for their extension. That feature was built successfully, but the implementation required some temporary workarounds:

• temporary private reflection code was required to remove scale monitors (code here).
• a custom IFunctionActivityStatusProvider hack had to be used to prevent premature drain mode completion for outstanding background workflows (code here).

We'll need to add first class features to support these scenarios better, so the workarounds can be removed.