feat(cli): add short description to bash completion

[vitorfloriano]

The completion for bash now displays the short description for the subcommands and flags, similar to the bash completion in tools like kubectl and helm.

The short descriptions provide better UX with improved discoverability. It will also allow us to add usage examples to the short descriptions in follow-ups.

Current bash completion:

$ kind
build       completion  create      delete      export      get         help        load        version

$ kind export
kubeconfig  logs

$ kind export kubeconfig --
--internal     --kubeconfig   --kubeconfig=  --name         --name=        --quiet        --verbosity    --verbosity=

Bash Completion V2:

$ kind
build       (Build one of [node-image])
completion  (Output shell completion code for the specified shell (bash, zsh or fish))
create      (Creates one of [cluster])
delete      (Deletes one of [cluster])
export      (Exports one of [kubeconfig, logs])
get         (Gets one of [clusters, nodes, kubeconfig])
help        (Help about any command)
load        (Loads images into nodes)
version     (Prints the kind CLI version)

$ kind export
kubeconfig  (Exports cluster kubeconfig)                              logs        (Exports logs to a tempdir or [output-dir] if specified)

$ kind export kubeconfig --
--help        (help for kubeconfig)
--internal    (use internal address instead of external)
--kubeconfig  (sets kubeconfig path instead of $KUBECONFIG or $HOME/.kube/config)
--name        (the cluster context name)
--quiet       (silence all stderr output)
--verbosity   (info log verbosity, higher value produces more output)

[stmcginnis]

spf13/cobra#1146 for background.

Simple update to the latest and greatest from the library. Looks good.

Some test failures, but that would not be related to this change.

/lgtm

[BenTheElder]

nice!!

looks like this is fully backwards compatible so
/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: BenTheElder, vitorfloriano

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