GitHub authentication for CI builds

[mavnn]

// cc @colinbull

Thanks for the awesome private github work. For things like CI servers and getting new developers set up, it would be great to be able to provide github credentials either via environment variables or in some form that can be commited to source control (I know there are dangers to this).

How do people feel is the best way to approach this? I really don't want to be relying on a user level config file for CI if at all possible.

[colinbull]

We currently, have CI accounts that we use against stash and github. So when we add a new build agent we just run paket config add credentials on that box. But you are right this is a PITA when moving to developers P.C's as they all have to have the same keys.

My personal feeling is that we should just extend the paket.config search path to look in the .paket folder for the paket.config file, if one exists then the credentials from here can be used. We would then add a switch to paket config to alter either a local or user level paket.config, whether or not this file gets committed to source is then at the discretion of the individual project.