Automate chart dependency and image tag updates using renovate

[chgl]

Is your feature request related to a problem? Please describe.

Updating the images used within the charts currently depends on manually created PRs to keep up-to-date with new images.

Describe the solution you'd like

Tools like renovatebot (https://github.com/renovatebot/renovate) can automatically create PRs for updating image tags and chart dependencies. To test it, I've enabled it in my fork: https://github.com/chgl/argo-helm/pull/1. For an example PR, see: https://github.com/chgl/argo-helm/pull/3.

Describe alternatives you've considered

Continue with ad-hoc updates via PRs from the community.

Additional context

The current downside is that it does not automatically bump the version field in Chart.yaml when updating image tag values. It does when updating sub-charts, though: renovatebot/renovate#4728. But this would at least allow for creating automated notifications if there's an update available upstream.

[chgl]

Small update: I've now got a PR goin' at renovatebot/renovate#8240 that would automatically bump the chart.yaml when image tags in values.yaml are updated. This should allow for completely automating the update process.

[github-actions]

Stale issue message