Support cli uninstall (#3399)

* Add uninstall cmd
- init fn to uninstall velero
- abstract dynamic client creation to a separate fn
- creates a separate client per unstructured resource
- add delete client for CRDs
- export appendUnstructured
- add uninstall command to main cmd
- export `podTemplateOption`
- uninstall resources in the reverse order of installation
- fallback to `velero` if no ns is provided during uninstall
- skip deletion if the resource doesn't exist
- handle resource not found error
- match log formatting with cli install logs
- add Delete fn to fake client
- fix import order
- add changelog
- add comment doc for CreateClient fn

Signed-off-by: Suraj Banakar <suraj@infracloud.io>

* Re-use uninstall code from test suite
- move helper functions out of test suite
- this is to prevent cyclic imports
- move uninstall helpers to uninstall cmd
- call them from test suite
- revert export of variables/fns from install code
- because not required anymore

Signed-off-by: Suraj Banakar <suraj@infracloud.io>

* Revert `PodTemplateOption` -> `podTemplateOption`

Signed-off-by: Suraj Banakar <suraj@infracloud.io>

* Use uninstall helper under VeleroUninstall
- as a wrapper
- fix import related errors in test suite

Signed-off-by: Suraj Banakar <suraj@infracloud.io>

test/e2e/enable_api_group_versions_test.go

@@ -23,6 +23,7 @@ import (
 
 	"github.com/vmware-tanzu/velero/pkg/builder"
 	veleroexec "github.com/vmware-tanzu/velero/pkg/util/exec"
+	"github.com/vmware-tanzu/velero/pkg/util/kube"
 )
 
 var _ = Describe("[APIGroup] Velero tests with various CRD API group versions", func() {
@@ -43,7 +44,7 @@ var _ = Describe("[APIGroup] Velero tests with various CRD API group versions",
 			"namespace": "cert-manager",
 		}
 
-		client, extensionsClient, err = GetClusterClient() // Currently we ignore the API extensions client
+		client, extensionsClient, err = kube.GetClusterClient() // Currently we ignore the API extensions client
 		Expect(err).NotTo(HaveOccurred())
 
 		err = InstallCRD(ctx, certMgrCRD["url"], certMgrCRD["namespace"])