Flux: Support arbitrary resources for "fluxcd.io/automated" annotation

[heprotecbuthealsoattac]

Describe the feature

It looks like fluxcd can't automatically update image for knative's service resource. I'd like fluxcd to be able to do that.
For reference:

ts=2019-10-15T16:44:21.722165052Z caller=kubernetes.go:147 warning="automation of this resource kind is not supported" resource=app:service/frontend

[squaremo]

It's not a huge leap to fluxd being able to update arbitrary resources -- there's already a scheme for pointing at the field to update, used for HelmRelease, which could be generalised.

_Today_, however, I think you would have to use Kustomize via .flux.yaml; but beware, there are problems with this approach (e.g., #2428).

[squaremo]

If you don't mind, I'm going to make this issue a little more general, since it's something we'd like to address for other kinds of custom resource.

[stefanprodan]

Duplicate of: #1794

[Morriz]

We would love to see this enhancement, which could modify and redeploy any resource matching the annotations.

[robinbraemer]

We also need this to work with CRDs! We are using Agones for instance and we
need the image to auto update for the GameServer in a Fleet.

Kustomize can already replace the image in CRs when generating yamls, so Flux should simply consider all resources with the fluxcd.io/automated: "true" annotation to trigger a release!

[robinbraemer]

Or the suggestion https://github.com/fluxcd/flux/issues/1794#issuecomment-628279100 would be easy to implement!