Create script to clear older caches (#18751)
Part of #17878
Summary of the issue:
PRs have been failing recently as we are well over our cache limit.
GitHub actions doesn't allow us to easily delete the caches of PR builds from within PRs, due to it being a cache poisoning risk.
Instead, we should clear caches manually on a regular basis.
Description of user facing changes:
None
Description of developer facing changes:
PRs more reliable
Description of development approach:
Use gh cli to fetch cache items
filter with jq for cache items last accessed older than 6 hours ago
delete filtered cache items
