Air-gapped support for tanzu-cli plugins

[anujc25]

Describe the feature request
Provide a means to migrate tanzu-cli plugins from the default oci registry to the private registry for the airgapped environment.

These can be done by implementing the following or equivalent commands.

• "tanzu plugin download-bundle" base command
• "tanzu plugin upload-bundle" base command

Additional things to do:

• Support plugin migration based on the plugin-group
• Verify the signature before downloading the plugin bundle
• Write E2E test for the air-gapped environments

Describe alternative(s) you've considered
None

Additional context