Introducing the TreeView component for DDF without React

[skateman]

• Maps the field value to checked nodes
• Maps checked nodes to the field value
• Loads the data using a promise function

{
  component: 'tree-view',
  name: 'foo',
  label: 'Foo',
  initialValues: [...],
  loadData: () => Promise,
  lazyLoadData: node => Promise,
}

AFAIK we're not doing lazyload in trees that are inside forms (except automate entrypoint selection), but better safe than sorry I implemented the behavior somehow. If it's undesired we can either change or remove it.

Fixes #6841

[miq-bot]

Checked commits skateman/manageiq-ui-classic@8a81560~...68c85d8 with ruby 2.6.3, rubocop 0.69.0, haml-lint 0.28.0, and yamllint
0 files checked, 0 offenses detected
Everything looks fine. 👍