Add "role" field to Contributors list in the oemetadata

[jh-RLI]

Description of the issue

The description of the role of a contributor can help to better understand the changes. This field is also supported/used in the frictionless data package spec.

Ideas of solution

Describe possible ideas for solution and evaluate advantages and disadvantages.

"contributors": [{
  "title": "Joe Bloggs",
  "email": "[email protected]",
  "path": "http://www.bloggs.com",
  "role": "author"
}]

Workflow checklist

• I am aware of the workflow in CONTRIBUTING.md