Clean up Go modules

[tenzen-y]

What this PR does / why we need it:
hack/swagger/go.mod is outdated. So, I performed go mod tidy.
Additionally, I added a CI command so that we can detect the outdated Go modules in CI.

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

Checklist:

• Docs included if any changes are user facing

[tenzen-y]

/assign @kubeflow/wg-training-leads

[coveralls]

Pull Request Test Coverage Report for Build 10587297012

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.02%) to 31.801%

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Totals
Change from base Build 10582250888:	0.02%
Covered Lines:	3950
Relevant Lines:	12421

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💛 - Coveralls

[terrytangyuan]

Thanks!

/lgtm
/approve

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

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