docs/reference/schema.md: Expand publisher object in schema table

[duncandewhurst]

Related issues

190

Description

This PR expands the publisher object in the schema reference table. It should have been done as part of #261

Merge checklist

• [x] Update the changelog (style guide)
• [ ] Run ./manage.py pre-commit to update derivative schema files, reference documentation and examples

If there are changes to network-schema.json, network-package-schema.json, reference/publication_formats/json.md, reference/publication_formats/geojson.md or guidance/publication.md#how-to-publish-large-networks, update the relevant manually authored examples:

• [ ] examples/json/:
  • [ ] network-package.json
  • [ ] api-response.json
  • [ ] multiple-networks.json
  • [ ] network-embedded.json
  • [ ] network-separate-endpoints.json
  • [ ] network-separate-files.json
  • [ ] nodes-endpoint.json
  • [ ] spans-endpoint.json
• [ ] examples/geojson/:
  • [ ] api-response.geojson
  • [ ] multiple-networks.geojson

If you used a validation keyword, type or format that is not already used in the schema:

• [ ] Update the list of validation keywords, types or formats in JSON Schema usage.
• [ ] Add a field that fails validation against the new keyword, type or format to network-package-invalid.json.
• [ ] Check that OFDS CoVE reports an appropriate validation error.

If you added a normative rule that is not encoded in JSON Schema:

• [ ] Update the list of other normative rules.
• [ ] Add a field that does not conform to the rule to network-package-additional-checks.json.
• [ ] Open a new issue to add an additional check to Lib Cove OFDS.

If there are changes to examples/geojson/nodes.geojson or examples/geojson/spans.geojson, check and update the data use examples:

• [ ] examples/leaflet/leaflet.ipynb
• [ ] examples/qgis/geojson.qgs