Support for printing the used version of the generator

[pomek]

📝 Provide a description of the improvement

🎯 Goals

• To learn a consumer the used pkg-gen version.

📗 Story

• Given: I am a developer who wants to learn which version of the tool I use.
• When: I execute npx ckeditor5-package-generator --help
• Or: I execute npx ckeditor5-package-generator --version
• Then: I would like to see the version number.

💡 Hints

• The --help flag could print in the footer section.

   npx ckeditor5-package-generator --help
   Usage: ckeditor5-package-generator [options] [packageName]
   
   Arguments:
     packageName           name of the package (@scope/ckeditor5-*)
   
   Options:
     -v, --verbose         output additional logs (default: false)
     --dev                 execution of the script in the development mode (default: false)
     --use-npm             whether use npm to install packages (default: false)
     --use-yarn            whether use yarn to install packages (default: false)
     --lang <lang>         programming language to use
     --plugin-name <name>  optional custom plugin name
     --version             ...
     -h, --help            display help for command
   
   Version: 1.0.0

• The --version flag could display it and finish the process.

   npx ckeditor5-package-generator --version
   1.0.0

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[pomek]

commander supports the #version() method so we can use it.