Add support for running helmfile on arbitrarily configured clusters

[jewee]

Currently helmfile composition generates kubernetes cluster context information for eks clusters via aws eks update-kubeconfig commands.
Previously if required variables to generate were missing the tool would run with default kubernetes context configured.

Since this has proven to be dangerous running against default context has been removed.
To be able to run helmfile composition against non eks clusters support for explicit context selection needs to be added in ops-cli