Container image isn't rebuilt on repository change

Describe the bug

When updating the container image repository (spec.build.output.image) in a KafkaConnect resource, the operator reports “Build configuration did not changed. Nothing new to build.”. While reading the source code, I stumbled over the strimzi.io/force-rebuild annotation, which seems to be undocumented - the image rebuilt successfully afterwards.

To Reproduce Steps to reproduce the behavior:

1. Change the build output image repository in spec.build.output.image
2. The operator will not trigger a rebuild (and push) of the image to the new repository

Expected behavior The operator should trigger a rebuild of the image and a rolling upgrade of the connectors.

Environment (please complete the following information):

• Strimzi version: 0.25.0
• Installation method: Helm chart
• Kubernetes cluster: Kubernetes 1.21
• Infrastructure: Amazon EKS

[scholzj]

We are always happy to accept contributions. I think the best way to fix this would be to append the information about the output to the existing build revision.

We plan to start working on the 0.26.0 release some time early next week. Is it important for you to have the fix in it? If yes, do you think you will have time for the PR to get it into it? If it is important for you and you are not sure you will be able to make it I can have a look at it as well. Otherwise I think we are fine to wait and just get it into some later release.

[juniorz]

Another reason for rebuilding is that after removing all references to the repo from the KafkaConnector resource, the user expects to be able to destroy the repository.

Not forcing a rebuild in order to create the image in the new repo breaks that expectation, because destroying the repo would cause any scheduling of replicas in nodes that don’t have the image cached to fail.