Adding CEL validations on v2 TrainJob CRD

[akshaychitneni]

What this PR does / why we need it:
This PR relates to #2209 adding CEL validations on TrainJob CRD. I will followup with validations implemented in webhook in separate PR

cc @andreyvelich @tenzen-y

[google-oss-prow]

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[tenzen-y]

Thanks for doing this.
I left my first feedback.

[tenzen-y]

Could you implement integration testing if these validations should work?
We can implement those tests in https://github.com/kubeflow/training-operator/tree/126110fd4d76439bd04ca9fdf96bafb7ea3b6910/test/integration/webhook.v2.

[coveralls]

Pull Request Test Coverage Report for Build 10893150232

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 10793288019:	0.0%
Covered Lines:	66
Relevant Lines:	66

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💛 - Coveralls

[tenzen-y]

/hold

[tenzen-y]

Additionally, could you sign DCO?