feat(cli): support CLI completion (backport #2017)

[mergify]

Description

enables the underlying cobra CLI completion scripts.

supported shells:

• Bash
• Zsh
• Fish
• PowerShell

this replaces (and un-hides) the previously-existing tendermint completion command that only supported bash & zsh.

see kava completion <shell> --help for specifics

❯ kava completion --help
Generate the autocompletion script for kava for the specified shell.
See each sub-command's help for details on how to use the generated script.

Usage:
  kava completion [command]

Available Commands:
  bash        Generate the autocompletion script for bash
  fish        Generate the autocompletion script for fish
  powershell  Generate the autocompletion script for powershell
  zsh         Generate the autocompletion script for zsh

Checklist

• Changelog has been updated as necessary.

---

This is an automatic backport of pull request #2017 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 8ac4c5d has failed:

On branch mergify/bp/release/v0.26.x/pr-2017
Your branch is up to date with 'origin/release/v0.26.x'.

You are currently cherry-picking commit 8ac4c5d0.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   CHANGELOG.md
	both modified:   cmd/kava/cmd/root.go

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally