Add additional query options to kepctl query

[jeremyrickard]

Currently, kepctl supports querying across KEPs on a few fields:

Examples:
  kepctl query --sig architecture --status provisional --include-prs

Flags:
      --gh-token-path string   Path to a file with a GitHub API token
  -h, --help                   help for query
      --include-prs            Include PRs in the results
      --output string          Output format. Can be [table json yaml] (default "table")
      --prr strings            Prod Readiness Approver
      --repo-path string       Path to kubernetes/enhancements
      --sig strings            SIG
      --stage strings          Stage
      --status strings         Status

Adding additional query options for --author and --approver would be beneficial additions. These should behave like the --prr flag.

/sig architecture
/priority important-soon