Add `plugin` command for managing plugins and their configs

[mostafa]

The idea is to have a plugin subcommand that can do a few things:

• [x] #265
• [x] #266
• [x] #264
• [x] #307
• [x] #309
• [ ] #350
• [ ] #475
  • This can be part of https://github.com/gatewayd-io/gatewayd-plugin-sdk/issues/1
  • [ ] plugin build: Build plugins
  • [ ] #183
  • [ ] Check plugin compatibility?
  • [ ] Generate the latest protobuf stubs for the given language
• [ ] #424

Requirements

• The plugins are supposed to be on GitHub for now, which means GitHub is the plugin registry for now, until the following feature is added:
  • https://github.com/gatewayd-io/internal-proposals/issues/8

Resources

• https://github.com/schollz/progressbar