chore(prow): add kind/feature label

[mrbobbytables]

Description

Adds a kind/feature label to .github/prow.yaml and lists it in the require_matching_label missing_comment. Feature requests such as #485 had no valid /kind to clear needs-kind (the author tried /kind feature-request and /kind enhancement, neither of which exists); the comment only offered failing-test and cleanup. label-sync runs on push to main when prow.yaml changes, so the label is created on merge.

Refs #485

Testing

Config-only change; no code paths touched.

• /kind feature on Add support for GitHub Groups to the Approve plugin #485 and feat(owners): support GitHub groups in OWNERS #486 after merge clears needs-kind (to be verified post-merge once label-sync has run)

Checklist

• I ran npm run all to lint and build my code — N/A, config only
• I ran npm run pack and committed dist/ — N/A, no src/ change
• Commits are signed off (DCO)
• Note any new dependencies these changes bring in — none
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas — N/A
• I have made corresponding changes to the documentation — missing_comment updated; no docs enumerate the repo's own kinds
• My changes generates no new warnings (please describe new warnings if unavoidable)