JSON schemas for Kometa YAML files

limitations:

- template variables not cased for specific default file
- template variables with keys are wildcarded
- "position" attribute has no validation
- "streaming" default has no validation
- search has no validation; just accepts string
- schedule has no validation; just accepts string

TODO:
"list of coordinates"

- schema for collection yaml
- schema for metadata yaml
- schema for overlay yaml
- schema for template yaml

Notes: