Support local packages in the enhanced YAML parser

[jimtng]

Could we also have local packages?

'.my_local_package':
  items:   
    ${name}:
      type: Switch
      label: ${label}
      icon: switch
      format: '%s'
      channel: mqtt:topic:${thing_id}:switch1


packages:
  obj1: !include
    local: .my_local_package  # <-- local instead of file
    vars: {name: "item_name1", label: "label1", thing_id: "thing1" }
  obj2: !include
    local: .my_local_package
    vars: {name: "item_name2", label: "label2", thing_id: "thing2" }

Originally posted by @spacemanspiff2007 in #4818 (comment)

[jimtng]

This is an interesting idea. It means we don't even need to pollute the file system with additional include files and keep everything in the main yaml file!