Move the litmus-service to keptn-contrib

[ksatchit]

The litmus-service has seen useful changes since the initial release (as can be gauged from these closed issues).

It has generated some positive community response (as seen from joint blogs and webinars) and seen initial adoption.

On behalf of the team working on this integration, would like to propose that litmus-service be moved to the next-stage of usage/recognition, i.e., be included into keptn-contrib.

We would be happy to understand any other requirements that need to be met for this and try to facilitate the same.

[ksatchit]

cc: @jetzlstorfer

[christian-kreuzberger-dtx]

FYI: https://github.com/keptn-sandbox/contributing#how-to-be-promoted-to-keptn-contrib-organization

In my opinion unit tests would be great before promoting to keptn-contrib.
edit: Example for unit tests: https://github.com/keptn-sandbox/keptn-service-template-go/blob/1562765b151bf008b083e4b543854d9600489555/eventhandler_test.go#L44-L78

Other then that, I'm happy to be the sponsor from the keptn core team. I like litmus-service and the way it works.