docs/reference/publication_formats/json.md: Fix broken schema browser

[duncandewhurst]

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Description
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This PR fixes the broken schema browser in https://open-fibre-data-standard.readthedocs.io/en/latest/reference/publication_formats/json.html#small-files-and-api-responses-option

Preview: https://open-fibre-data-standard.readthedocs.io/en/network-package-schema-browser/reference/publication_formats/json.html#small-files-and-api-responses-option

Merge checklist

• 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
• Run ./manage.py pre-commit to update derivative schema files, reference documentation and examples
• 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]((https://ofds-standard-development-handbook.readthedocs.io/en/latest/standard/schema.html#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
• Update the changelog (style guide)

[duncandewhurst]

I think that we can merge this into 0.1 without creating a new tagged release as it's just a fix to how the docs site renders. We can then merge 0.1 into 0.1-dev so that they are not out of sync.

As you can see, I encountered some challenges getting this to work because it behaves differently locally and on ReadTheDocs and because I didn't realise that the two URLs are relative to different locations: Open-Telecoms-Data/standard-development-handbook#22