Add new(?) kube-webhook-certgen tag

[cwayne18]

Pull Request Checklist

• Change does not remove any existing Images or Tags in the images-list file
• Change does not remove / overwrite exiting Images or Tags in Rancher DockerHub
• If updating an existing entry, verify the SOURCE is still accurate and upstream hasn't been migrated to a new regitry or repo (if they've migrated, a new repo request to EIO is needed to comply with the SOURCE DESTINATION TAG pattern)
• New entries are in format SOURCE DESTINATION TAG
• New entries are added to the correct section of the list (sorted lexicographically)
• New entries have a repo created in Rancher Dockerhub (where the image will be mirrored to)
• New entries are licensed with Rancher favored licenses - Apache 2 and MIT - or approved licenses - as according to CNCF approved licenses.
• New entries, when used in Rancher or Rancher's provided charts, have their corresponding origin added in Rancher's images origins file (must be added for all Rancher versions >= v2.7).
• Changes to scripting or CI config have been tested to the best of your ability

Types of Change

Linked Issues

Additional Notes

Final Checks after the PR is merged

• Confirm that you can pull the new images and tags from DockerHub