Retriever config for Kubernetes that doesn't hardcode secret

[jml]

A couple of times over the last few days I've been pinged by people who have been confused by the cortex retrieval example in the sockshop, which hardcodes a dummy, broken value for the Weave Cloud access token.

It might be nice, as part of Cortex or something else, to provide an image that takes the access token as a command line or environment variable, and a set of Kubernetes configurations that use that image rather than prometheus.

Pro:

• easier onboarding for newcomers to prometheus

Con:

• masks the fact that retrievers really are vanilla prometheus
• maybe makes our messaging more confusing for existing prometheus users

[bboreham]

Fixed by microservices-demo/microservices-demo#385 and the Launch Generator