Enable portal editing for Linux

[This was cut from the Linux preview scope but is required for a compelling scripting (Python / PowerShell / Node) story.]

**Problem Statement:**
The portal editing experience for Linux depends on Azure Files, which takes a while to get provisioned.This creates a perception that the Function App provisioning itself is either too slow or completely broken.

**Proposed Solution**
Make portal editing an explicit gesture that a user opts into from the quick-start, at which point we provision the Azure Files.