Process image lines concurrently, 10 at a time

[dereknola]

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

Instead of sequentially processing each image line (most of which are old versions and no-op), allow 10 concurrent processes to work on a line. This should dramatically improve performance of the script times.

Linked Issues

Additional Notes

Final Checks after the PR is merged

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

[github-actions]

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