expose yaml context above `panels:` to jinja

[maxheld83]

dashboards:
  foo: 1
  - name: Lorem
    bar: 2
    panels:
      baz: 3
      - title: Ipsum
    type: jinja2
    template: {{ dashboards.foo }} {{ dashboards.lorem.bar }} {{ panel.baz }}

Currently (as documented), from the above template, only panel.baz is available to jinja2.

For greater DRY it'd be great to be able to use variables from higher up in the YAML.

(My use case: reusing query components).