Simplify Airgap image installs

[dereknola]

Is your feature request related to a problem? Please describe.
When installing additional CNIs for airgap, you must manually copy any/all rke2-images-${CNI}.${ARCH}.tar.gz to /var/lib/rancher/rke2/agent/images.

Describe the solution you'd like
Expand the existing install script, which already copies rke2-images.${ARCH}.tar.gz from the RKE2_ARTIFACTS_PATH, to also copy any additional rke2-images-XXXXX found in that folder.

Describe alternatives you've considered

Additional context

[mdrahman-suse]

Validated using the RCs

Example with v1.28.13-rc2+rke2r1 with Window agent

$ ls -la artifacts/
total 1217408
drwxr-xr-x 2 ubuntu ubuntu       4096 Aug 23 22:28 .
drwxr-x--- 5 ubuntu ubuntu       4096 Aug 23 22:28 ..
-rw-r--r-- 1 ubuntu ubuntu  121689804 Aug 23 22:22 rke2-images-flannel.linux-amd64.tar.gz
-rw-r--r-- 1 ubuntu ubuntu 1090910209 Aug 23 22:22 rke2-images.linux-amd64.tar.gz
-rw-r--r-- 1 ubuntu ubuntu   34004119 Aug 23 22:22 rke2.linux-amd64.tar.gz
-rw-r--r-- 1 ubuntu ubuntu       3939 Aug 23 22:22 sha256sum-amd64.txt

~$ sudo INSTALL_RKE2_ARTIFACT_PATH=artifacts/ sh rke2-install.sh
[INFO]  staging local checksums from artifacts//sha256sum-amd64.txt
[INFO]  staging gzip airgap image tarball from artifacts//rke2-images.linux-amd64.tar.gz
[INFO]  staging tarball from artifacts//rke2.linux-amd64.tar.gz
[INFO]  verifying airgap tarball
[INFO]  decompressing airgap tarball to /var/lib/rancher/rke2/agent/images
[INFO]  Installing airgap image from artifacts//rke2-images-flannel.linux-amd64.tar.gz
[INFO]  verifying tarball
[INFO]  unpacking tarball file to /usr/local

$ ls -la /var/lib/rancher/rke2/agent/images/
total 3195240
drwxr-xr-x 2 root root       4096 Aug 23 22:38 .
drwxr-xr-x 3 root root       4096 Aug 23 22:37 ..
-rw-r--r-- 1 root root  121689804 Aug 23 22:38 rke2-images-flannel.linux-amd64.tar.gz
-rw-r--r-- 1 root root 3150215680 Aug 23 22:38 rke2-images.linux-amd64.tar

$ kgn
NAME               STATUS   ROLES                       AGE   VERSION
ip-172-31-22-136   Ready    control-plane,etcd,master   33m   v1.28.13+rke2r1
ip-ac1f2610        Ready    <none>                      97s   v1.28.13

$ kgp
NAMESPACE     NAME                                                   READY   STATUS      RESTARTS   AGE
kube-system   cloud-controller-manager-ip-172-31-22-136              1/1     Running     0          25m
kube-system   etcd-ip-172-31-22-136                                  1/1     Running     0          26m
kube-system   helm-install-rke2-coredns-njmtt                        0/1     Completed   0          26m
kube-system   helm-install-rke2-flannel-rpnv2                        0/1     Completed   0          26m
kube-system   helm-install-rke2-ingress-nginx-6bnlg                  0/1     Completed   0          26m
kube-system   helm-install-rke2-metrics-server-74c7h                 0/1     Completed   0          26m
kube-system   helm-install-rke2-snapshot-controller-7zg9t            0/1     Completed   1          26m
kube-system   helm-install-rke2-snapshot-controller-crd-jwjbs        0/1     Completed   0          26m
kube-system   helm-install-rke2-snapshot-validation-webhook-sjbld    0/1     Completed   0          26m
kube-system   kube-apiserver-ip-172-31-22-136                        1/1     Running     0          26m
kube-system   kube-controller-manager-ip-172-31-22-136               1/1     Running     0          26m
kube-system   kube-flannel-ds-cxxhc                                  1/1     Running     0          26m
kube-system   kube-proxy-ip-172-31-22-136                            1/1     Running     0          26m
kube-system   kube-scheduler-ip-172-31-22-136                        1/1     Running     0          25m
kube-system   rke2-coredns-rke2-coredns-autoscaler-db75d9cdc-vgzxq   1/1     Running     0          26m
kube-system   rke2-coredns-rke2-coredns-b97fb45df-bzhmq              1/1     Running     0          26m
kube-system   rke2-ingress-nginx-controller-mkppk                    1/1     Running     0          25m
kube-system   rke2-metrics-server-655477f655-jtv67                   1/1     Running     0          25m
kube-system   rke2-snapshot-controller-59cc9cd8f4-jxbsb              1/1     Running     0          25m
kube-system   rke2-snapshot-validation-webhook-54c5989b65-z4xrp      1/1     Running     0          25m

[dereknola]

We should be able to do something similar. Opening a separate ticket would be best.