Cache helm client files

test-on-cng requires a few external chart installation. This makes it dependant on upstream sources which can periodically fail, like so:

=== block 'running pre-deployment setup' error ===
Command 'helm package --dependency-update --destination /tmp/cng20241219-21-fgqjs3/gitlab-555aff3d2ae9c36e936e8a30b0376a765bea00d0 /tmp/cng20241219-21-fgqjs3/gitlab-555aff3d2ae9c36e936e8a30b0376a765bea00d0' failed!
Error: could not download https://charts.jetstack.io/charts/cert-manager-v1.12.14.tgz: Get "https://charts.jetstack.io/charts/cert-manager-v1.12.14.tgz": EOF
=== block 'running pre-deployment setup' error ===

Investigate options to cache these files. One options could be overriding XDG_CACHE_HOME variable.

This variable is common and could interfere with other tools, so potentially implementing separate option in cng orchestrator might be necessary