[FLINK-37769] Include cause in event when restarting unhealthy job

[darenwkt]

What is the purpose of the change

This PR is a feature improvement to include cause in event when restarting unhealthy job:

Before:

2025-05-15 14:08:52,863 o.a.f.k.o.l.AuditUtils         [INFO ][default/basic-example] >>> Event[Job]       | Warning | RESTARTUNHEALTHYJOB | Restarting unhealthy job

After:

2025-05-15 14:08:52,863 o.a.f.k.o.l.AuditUtils         [INFO ][default/basic-example] >>> Event[Job]       | Warning | RESTARTUNHEALTHYJOB | Restart count hit threshold: 1

Brief change log

• A new class ClusterHealthResult is introduced to store information about the job health and error message

Verifying this change

This change added unit tests and can be verified as follows:

• Manually built image and run on local minikube
• Verified ClusterHealthResult is serialised and deserialised correctly by observer

2025-05-15 14:09:50,968 o.a.f.k.o.o.ClusterHealthObserver [DEBUG][default/basic-example] Observed cluster health: ClusterHealthInfo(timeStamp=1747318190968, numRestarts=0, numRestartsEvaluationTimeStamp=0, numCompletedCheckpoints=0, numCompletedCheckpointsIncreasedTimeStamp=0, healthResult=ClusterHealthResult(healthy=true, error=null))

• Verified Event created contains caused of unhealthy job

2025-05-15 14:08:52,863 o.a.f.k.o.l.AuditUtils         [INFO ][default/basic-example] >>> Event[Job]       | Warning | RESTARTUNHEALTHYJOB | Restart count hit threshold: 1

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (no)
• The public API, i.e., is any changes to the CustomResourceDescriptors: (no)
• Core observer or reconciler logic that is regularly executed: (yes)

Documentation

• Does this pull request introduce a new feature? (no)
• If yes, how is the feature documented? (not applicable)

[darenwkt]

Hi @gyfora, would you be able to review this PR please? Thank you

[darenwkt]

Thanks @gyfora for the review, I have addressed the comments, could you take another look please? Thank you

[gyfora]

Added a minor test comment, after that it should be good to go :)

[darenwkt]

Thanks @gyfora, addressed comment :)