Backend - Added modern time formatters

[Ark-kun]

Placeholder format: {{$.scheduledTime.strftime('%Y-%m-%d')}}

[google-oss-robot]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[Ark-kun]

/test kubeflow-pipeline-backend-test

[Bobgy]

@Ark-kun thank you! This is awesome 😎

Do you need any help finishing this?

[Ark-kun]

Sorry for the delay. Fixed the regex bug.
The backend test now passes.

[Bobgy]

Thank you so much!
I will review next week

[Bobgy]

/lgtm
/approve
Good point, we can change time zone in a separate PR

[google-oss-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Bobgy

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