Implement Patches update strategy for ImageUpdateAutomation resource

[Tzrlk]

Since comments may not necessarily be preserved in some image pipelines, and keeping necessary configuration in comments is generally considered to be a bad code smell, Patches should be added to the list of available options when setting spec.update.strategy on ImageUpdateAutomation resources, and a field added to contain the list of parameterised patches needed to update the relevant fields.

e.g.

apiVersion: image.toolkit.fluxcd.io/v1beta1
kind:       ImageUpdateAutomation
spec:
  update:
    strategy: JSONPatches
    path:     /apps/nginx/_base
    patches:
      - target:
          kind: Deployment
        patches:
          - path: /spec/containers/*/image
            replace: 'nginx:$1' # implied filter of '^.+$'
          - path: /metadata/labels/app.kubernetes.io~1version
            select: '^v([\\d\\.]+)' # implied termplate of '$1'

These patches would work exactly like Kustomize patches, except that the value can be run through a regex beforehand, and the operation is assumed to be "replace".

[kingdonb]

I do think this is a great idea and well argued, I think we are considering which features to add in the context of separating ideas into before-GA and after-GA, I think as a new feature this sounds like one that would likely come after Flux 2.0 or GA.

Thanks for the suggestion!

[tskinner-oppfi]

Now that Flux 2.0 is pretty close to release what are the current thoughts on this? This is sorely needed for my setup and I'm happy to contribute some code.

[makkes]

Getting this implemented will definitely take some time and it should be initiated by an RFC. Before that happens, though, I believe it makes sense to haul in the other maintainers. @tskinner-oppfi would you like to join the next weekly meeting and bring this issue forward?