unmanaged-cluster: support no CNI and failed CNI

[joshrosso]

What this PR does / why we need it

This commit adds support for creating clusters without installing CNI. It
also enables cluster creation to complete successfully when a CNI
package fails to resolve.

For creating clusters without CNI, a user may set the CNI configuration
value to "none". For example, cluster creation can occur as follows:

tanzu uc create testme --cni=none

Users will receive a warning message that no CNI was installed, and the
installation will complete.

For when a CNI is specified but is invalid, for example:

tanzu uc create testme --cni=beepboopnotreal

Users will receive a warning message that no CNI package was found, but
the install will still complete. This is because the cluster is still
successfully started and the user could choose to remedy or troubleshoot
after bootstrapping.

Details for the Release Notes (PLEASE PROVIDE)

unmanaged-clusters support none for CNI value, preventing an install of CNI after cluster creation.

Which issue(s) this PR fixes

Fixes: #2939
Fixes: #2940

Describe testing done for PR

CNI does not install when set to none ✔️.

CNI skipped when cannot resolve package (rather than fail) ✔️

CNI Selection still works as expected ✔️

Special notes for your reviewer

None

[jpmcb]

I'm guessing you didn't mean to commit either of these files?

• cli/cmd/plugin/unmanaged-cluster/test.png
• docs/site/.hugo_build.lock
• cli/cmd/plugin/unmanaged-cluster/--help

---

Otherwise, code in tanzu.go looking good!

[jpmcb]

Default behavior still works ✅

Selecting none CNI works ✅

❯ k get pods -A
NAMESPACE            NAME                                                 READY   STATUS    RESTARTS   AGE
kube-system          coredns-558bd4d5db-4r8bj                             0/1     Pending   0          116s
kube-system          coredns-558bd4d5db-fp9jd                             0/1     Pending   0          116s
kube-system          etcd-test-cluster-control-plane                      1/1     Running   0          118s
kube-system          kube-apiserver-test-cluster-control-plane            1/1     Running   0          118s
kube-system          kube-controller-manager-test-cluster-control-plane   1/1     Running   0          118s
kube-system          kube-proxy-6m6pf                                     1/1     Running   0          116s
kube-system          kube-scheduler-test-cluster-control-plane            1/1     Running   0          118s
local-path-storage   local-path-provisioner-547f784dff-xg4x8              0/1     Pending   0          116s
tkg-system           kapp-controller-f7dbbcb4f-hp5jl                      1/1     Running   0          113s

Non-resolving CNI works ✅

Setting a valid CNI works ✅

This is amazing!!!

[joshrosso]

I'm guessing you didn't mean to commit either of these files?

• cli/cmd/plugin/unmanaged-cluster/test.png
• docs/site/.hugo_build.lock
• cli/cmd/plugin/unmanaged-cluster/--help

Otherwise, code in tanzu.go looking good!

I did not, removed those files 👍.

Ready for approve/merge.