Add remote debugging for node functions on Linux dedicated plans

[mrcrane]

This is the first step to bring the App Services remote debugging experience to Functions.

Remote debugging requires two main pieces to be in place on the Azure side:

• The tunnel API needs to be available on Kudu.
• The runtime needs to launch in debug mode and configure the tunnel when the "remoteDebuggingEnabled" config is set.

The configuration piece has been taken care of here: Azure/azure-functions-docker#107

The Kudu tunnel API is currently only available on Linux dedicated plans. We have started the conversation about enabling the tunneling API for Linux consumption plans, but this is non-trivial work that will take some time.

This issue covers the work for Linux dedicated plans, which will give us a quick win and allow us to iron out all of the tooling issues. Once we have nailed down the experience with dedicated plans, we will be in a good place to add support for consumption plans when they become available.

[mrcrane]

• The first step is to get the remote debug code into a place that it can be reused by functions.
  • See PR here: Refactor remote debugging commands into common library so we can support functions vscode-azuretools#522
• After this we can update the functions extension to use the shared code
  • We will need to figure out how this will coexist with the existing, older Java remote debugging functionality. See: https://github.com/Microsoft/vscode-azurefunctions/wiki/Remote-Debug-Java-functions
  • For now we can just give it a separate experiment feature flag. The Java feature is experimental and is hidden behing the config "azureFunctions.enableRemoteDebugging": true. We can add a new flag such as "azureFunctions.enableNodeRemoteDebugging": true which enables this feature separately. This puts us in a place where we can test these features independently.
  • I will sync up with @fiveisprime to come up with a long term plan to merge with or replace the Java feature.