Remove invocation with "kubernetes" in the help

[marckhouzam]

What this PR does / why we need it

Today plugins created with TargetK8s target type have their commands visible/invocable via both tanzu <pluginname> ... and tanzu kubernetes|k8s <plugingname> ...

The form without a target prefix is available only to kubernetes target for historical and compatibility reasons, but is the predominant invocation style. Since Tanzu Platform's plugin functionality are delivered through a mix of kubernetes-targeted and nonkubernetes-targeted plugins, encouraging this more compact form is important in promoting consistent and intuitive invocation styles.

This PR removes the invocation using the kubernetes target from the help output of plugins.

Note that a plugin must be recompiled with this PR for the change to take effect. Therefore it will only start taking effect as new versions of plugins get released.

Which issue(s) this PR fixes

Fixes #

Describe testing done for PR

Note that I'm using the CLI build with vmware-tanzu/tanzu-cli#781 which adds a deprecation message for the invocation with the kubernetes target prefix.

Before the change this was the output of the help for the services plugin which has a target of kubernetes:

Commands for working with services, classes and claims

Usage:
  tanzu services [command]
  tanzu kubernetes services [command]

Aliases:
  services, service

Available Commands:
  bind          Bind a service to an app
  create        Create a new service
  delete        Delete a service
  get           Get a service
  list          List the available services
  type          Commands for working with service types
  unbind        Unbind a service from an app

Flags:
      --context string      name of the kubeconfig context to use (default is current-context defined by kubeconfig)
  -h, --help                help for services
      --kubeconfig string   kubeconfig file (default is /Users/kmarc/.kube/config)
      --no-color            turn off color output in terminals

Use "tanzu services [command] --help" for more information about a command.
Use "tanzu kubernetes services [command] --help" for more information about a command.
$ tz k8s services -h
Command "services" is deprecated, when called with the "kubernetes" prefix. Please invoke "services" directly without the "kubernetes" prefix.
Commands for working with services, classes and claims

Usage:
  tanzu services [command]
  tanzu kubernetes services [command]

Aliases:
  services, service

Available Commands:
  bind          Bind a service to an app
  create        Create a new service
  delete        Delete a service
  get           Get a service
  list          List the available services
  type          Commands for working with service types
  unbind        Unbind a service from an app

Flags:
      --context string      name of the kubeconfig context to use (default is current-context defined by kubeconfig)
  -h, --help                help for services
      --kubeconfig string   kubeconfig file (default is /Users/kmarc/.kube/config)
      --no-color            turn off color output in terminals

Use "tanzu services [command] --help" for more information about a command.
Use "tanzu kubernetes services [command] --help" for more information about a command.
$ tz services list -h
List the available services

Usage:
  tanzu services list [flags]
  tanzu kubernetes services list [flags]

Examples:
  tanzu services list

Flags:
  -h, --help   help for list

Global Flags:
      --context string      name of the kubeconfig context to use (default is current-context defined by kubeconfig)
      --kubeconfig string   kubeconfig file (default is /Users/kmarc/.kube/config)
      --no-color            turn off color output in terminals

After recompiling the plugin using a plugin-runtime with this PR, the help no longer shows the invocation with kubernetes:

$ tz services -h
Commands for working with services, classes and claims

Usage:
  tanzu services [command]

Aliases:
  services, service

Available Commands:
  bind          Bind a service to an app
  create        Create a new service
  delete        Delete a service
  get           Get a service
  list          List the available services
  type          Commands for working with service types
  unbind        Unbind a service from an app

Flags:
      --context string      name of the kubeconfig context to use (default is current-context defined by kubeconfig)
  -h, --help                help for services
      --kubeconfig string   kubeconfig file (default is /Users/kmarc/.kube/config)
      --no-color            turn off color output in terminals

Use "tanzu services [command] --help" for more information about a command.

$ tz k8s services -h
Command "services" is deprecated, when called with the "kubernetes" prefix. Please invoke "services" directly without the "kubernetes" prefix.
Commands for working with services, classes and claims

Usage:
  tanzu services [command]

Aliases:
  services, service

Available Commands:
  bind          Bind a service to an app
  create        Create a new service
  delete        Delete a service
  get           Get a service
  list          List the available services
  type          Commands for working with service types
  unbind        Unbind a service from an app

Flags:
      --context string      name of the kubeconfig context to use (default is current-context defined by kubeconfig)
  -h, --help                help for services
      --kubeconfig string   kubeconfig file (default is /Users/kmarc/.kube/config)
      --no-color            turn off color output in terminals

Use "tanzu services [command] --help" for more information about a command.

$ tz services list -h
List the available services

Usage:
  tanzu services list [flags]

Examples:
  tanzu services list

Flags:
  -h, --help   help for list

Global Flags:
      --context string      name of the kubeconfig context to use (default is current-context defined by kubeconfig)
      --kubeconfig string   kubeconfig file (default is /Users/kmarc/.kube/config)
      --no-color            turn off color output in terminals

Release note

No longer show the invocation with the `kubernetes` target prefix in the help output.

Additional information

Special notes for your reviewer

[vuil]

lgtm, thanks!