[GSoC] New Interface report_metrics in Python SDK

[Electronic-Waste]

What this PR does / why we need it:

I add a new interface report_metrics in Python SDK. Design details: https://github.com/kubeflow/katib/blob/4161cff0faf7700598489f1fbaa5346b948623e2/docs/proposals/push-based-metrics-collection.md#new-interface-report_metrics-in-python-sdk

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

Checklist:

• Docs included if any changes are user facing

[Electronic-Waste]

ref issue: #2340

[andreyvelich]

Thank you for adding this @Electronic-Waste!
I added a few comments.
/assign @gaocegege @johnugeorge @tenzen-y

[Electronic-Waste]

@andreyvelich I made the following changes as you requested after the meeting yesterday:

• A validation function for metrics value in utils.py
• Check the values in dict[str, Any] in report_metrics
• Rename katib_report_metrics.py to report_metrics.py

Can you take a look when you are free? Thanks a lot!

[andreyvelich]

Thanks @Electronic-Waste, I just added a few nits.
/assign @johnugeorge @tenzen-y

[andreyvelich]

Thank you @Electronic-Waste!
/lgtm
/assign @johnugeorge @tenzen-y

[andreyvelich]

I think, we should be ready to merge it.
/approve

[google-oss-prow]

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