Need to provide a way for developers to test with Edge pre-prod/integration.

Proposed solution: expose a new configuration key for the Experience Edge testing environment only for development, that can be set using MobileCore.updateConfig API.
Edge extension reads this key from config and does the mapping to the correct endpoint. By default, if this key is not present or it is not one of the expected values, it falls back to prod.

This key will not be exposed in Launch UI.

e.g. "edge.environment" = String in ("prod", "pre-prod", "int")