Support redirection for organizations with multiple project repos

[alexellis]

Expected Behaviour

A setting should be made available to .DEREK.yml which means Derek will redirect and pull his config from another location. We should probably enforce some basic validations here and I'm open to suggestions.

Current Behaviour

We maintain separate config files per repo within the organization of openfaas / openfaas-incubator

Possible Solution

Add a tag to the YAML which overrides the behavior to load the current file.

Context

OpenFaaS contributors have required this

Your Environment

• [x] You're using the hosted Derek service

or

• [x] You host your own OpenFaaS cluster with Derek installed

[alexellis]

cc @iyovcheva

[alexellis]

Derek close: implemented and merged