fix: update strfmt duration parsing

[bernot-dev]

Update pkg/validation/strfmt/duration.go to backport the duration parsing improvements from upstream github.com/go-openapi/strfmt@v0.26.4.

Specifically, this makes validation more strict and performant. See: go-openapi/strfmt#246

Unrecognized tokens that do not correspond to a known duration will cause the format to be deemed invalid.

[kubernetes-prow]

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[Jefftree]

LGTM

/cc @liggitt

Didn't get time to finish my previous attempt in #552, this should address the concerns you raised there. It backports go-openapi's parser, so the junk-skipping is gone. One note is that it still intentionally tolerates a space after the sign (- 5s), which I think should be fine?