Support "tanzu cluster get" on TKGS clusters.

[saimanoj01]

Bug description
Once the CAPI core is bumped to v1beta1, tanzu cluster get on TKGS will be broken. This is due to that fact that the API types supported by TKGm and TKGS are diverging. TKGm is moving to v1beta1 while TKGS still remains on v1alpha3.

Since CAPI v1.0.0 still supports querying clusters using the v1alpha3 API type we were able to branch out and have separate logic to manage TKGm and TKGS clusters.
Get Machine Deployments for TKGS - https://github.com/saimanoj01/tanzu-framework/blob/capi_v1beta1/pkg/v1/tkg/client/client.go#L155

Get Machine deployments for TKGm - https://github.com/saimanoj01/tanzu-framework/blob/capi_v1beta1/pkg/v1/tkg/client/client.go#L152

But this won't work for the tanzu get cluster command because we rely on the DescribeCluster API from the upstream CAPI v1.0.0. The problem with that API is that, it always queries for v1beta1 objects and there is no provision to query v1alpha3 based clusters and hence we can't use the same API for both TKGm and TKG clusters.
https://github.com/kubernetes-sigs/cluster-api/blob/release-1.0/cmd/clusterctl/client/tree/discovery.go#L50

The error we are seeing when we execute the tanzu cluster get command TKGS clusters.

$ ./artifacts/darwin/amd64/cli/cluster/v0.6.0-dev/tanzu-cluster-darwin_amd64  get tkgs-wc-one -n test-gc-e2e-demo-ns
I1103 21:46:53.705532   29683 request.go:665] Waited for 1.12895738s due to client-side throttling, not priority and fairness, request: GET:https://192.168.123.2:6443/apis/nsx.vmware.com/v1alpha1?timeout=32s
Error: no matches for kind "Cluster" in version "cluster.x-k8s.io/v1beta1"

Affected product area (please put an X in all that apply)

• APIs
• Addons
• CLI
• Docs
• IAM
• Installation
• Plugin
• Security
• Test and Release
• User Experience

Expected behavior
tanzu cluster get should work for TKGS clusters.

Steps to reproduce the bug

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Environment where the bug was observed (cloud, OS, etc)

Relevant Debug Output (Logs, manifests, etc)