feat: add scaffold command

[suzuki-shunsuke]

#922

$ aqua help gr
NAME:
   aqua generate-registry - Generate a registry's package configuration

USAGE:
   aqua generate-registry <package name>

DESCRIPTION:
   Generate a template of Registry package configuration.
   
   Note that you probably fix the generate code manually.
   The generate code is not perfect and may include the wrong configuration.
   It is just a template.
   
   e.g.
   
   $ aqua gr cli/cli # Outputs the configuration.
   packages:
     - type: github_release
       repo_owner: cli
       repo_name: cli
       asset: gh_{{trimV .Version}}_{{.OS}}_{{.Arch}}.{{Format}}
       format: tar.gz
       description: GitHub’s official command line tool
       replacements:
         darwin: macOS
       overrides:
         - goos: windows
           format: zip
       supported_envs:
         - darwin
         - linux
         - amd64
       rosetta2: true

e.g.

$ aqua gr cli/cli
packages:
  - type: github_release
    repo_owner: cli
    repo_name: cli
    asset: gh_{{trimV .Version}}_{{.OS}}_{{.Arch}}.{{Format}}
    format: tar.gz
    description: GitHub’s official command line tool
    replacements:
      darwin: macOS
    overrides:
      - goos: windows
        format: zip
    supported_envs:
      - darwin
      - linux
      - amd64
    rosetta2: true

⚠️ Future work

I tried to implement the insert option -i, but it doesn't work well.