Remove need for duplication between ct.yaml and the release GH action

[plumdog]

Both have to know about the chart repos for the chart dependencies, so need to be kept in sync. There might be a nicer way, but helm/chart-releaser#135 suggests maybe not.

Maybe something faintly bonkers like:

yq -r '.chart-repos[]' ct.yaml | sed 's/=/ /' | xargs -L helm repo add

in the release action is OK.

[matthewelwell]

@plumdog I see that we merged a PR against this one above - can we resolve this issue?

[plumdog]

@matthewelwell the merged PR is the sad "just define the repos in two places to fix the brokenness" fix. This issue is about removing that duplication.