Add buf registry plugin label commands

[emcfarlane]

This adds buf registry plugin label {archive,info,list,unarchive} commands to manage BSR plugin labels.

The trimmed output of buf plugin registry label --help:

Manage a plugin's labels

Usage:
  buf registry plugin label [flags]
  buf registry plugin label [command]

Available Commands:
  archive     Archive a plugin label
  info        Show label information
  list        List plugin labels
  unarchive   Unarchive a plugin label

[github-actions]

The latest Buf updates on your PR. Results from workflow Buf CI / buf (pull_request).

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Dec 3, 2024, 9:30 PM