[Release-1.28] - Allow configuration of Rootlesskit's CopyUpDirs through an environment variable

[brandond]

Backport fix for Allow configuration of Rootlesskit's CopyUpDirs through an environment variable

• Allow configuration of Rootlesskit's CopyUpDirs through an environment variable #10385

[mdrahman-suse]

Validated on release-1.28 branch with commit 914f1d9

Steps: #11006 (comment)

Validation

$ k3s -v
k3s version v1.28.14+k3s-914f1d91 (914f1d91)
go version go1.22.6

$ kubectl exec -it pod/basic -- ls my_share
pretest.txt
$ kubectl exec -it pod/basic -- touch my_share/hellop2l.txt
$ kubectl exec -it pod/basic -- ls my_share
hellop2l.txt  pretest.txt
$ ls containerShare/
pretest.txt