Allow parameterisation of launcher via helm chart

[bboreham]

From a user on Slack:

I wish I can feed it these values on start https://github.com/fluxcd/flux/blob/master/chart/flux/values.yaml#L4 cause we have them set per env via git already (for OSS)

The context was, someone who prefers to configure things via helm chart is at a disadvantage with the current launcher agent which has a CLI and Deployment yaml.

They were previously using OSS Flux via that chart, so see conversion to Weave Cloud as a change to that config.

[bboreham]

TIL there is a helm chart: https://github.com/helm/charts/tree/master/stable/weave-cloud

[bboreham]

Changed the title to focus this issue on how to get the end-user's desired configuration into some helm chart(s) which will then govern how the system behaves.