Reorganize the content of the Devfile reference on the model on what we did for the Devfile 2 documentation

• See the PR introducing the changes in the devfile/docs repository: https://github.com/devfile/docs/pull/27
• See the new story after revamp: https://docs.devfile.io/devfile/user-guide/authoring-stacks.html
• New story name: Authoring stacks
• Navigation per section in the YAML:
  • Adding schema version
  • Adding a name
  • Adding projects
  • Adding commands
  • Adding components
    • Adding plugin component
    • Adding kubernetes component
    • Adding container component
    • Specifying persistent storage
    • Limiting resources usage
    • Defining environment variables
    • Defining endpoints
    • Defining Kubernetes resources
  • Adding attributes
  • WARNING: don't add devfile v2 specific sections: Adding event bindings and Refering to a parent

• Content of each section is a procedure with steps.
• Use example blocks for examples.
• NOTE: in devfile/docs, we removed all references to che-docs, it is not necessary to remove these references in che-docs.
• NOTE: in devfile/docs, we didn't pay much attention to anything else than metadata and the structure of the docs. More improvements  on content and language are welcome.