fix(operator): Prevent JobSet recreation when its TTL has expired

[astefanutti]

What this PR does / why we need it:

Prevent the recreation of the JobSet when its TTL duration has expired.

Fixes #2981

Checklist:

• Docs included if any changes are user facing

[google-oss-prow]

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[coveralls]

Pull Request Test Coverage Report for Build 19742327386

Details

• 0 of 10 (0.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.2%) to 51.264%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/controller/trainjob_controller.go	0	1	0.0%
pkg/util/trainjob/trainjob.go	0	4	0.0%
pkg/runtime/framework/plugins/jobset/jobset.go	0	5	0.0%

Totals
Change from base Build 19741789363:	-0.2%
Covered Lines:	1237
Relevant Lines:	2413

---

💛 - Coveralls

[astefanutti]

/assign @kubeflow/kubeflow-trainer-team