Add tender.datePublished

[neelima-j]

Related issues

Closes #286

Description

Merge checklist

• Log your changes

If there are changes to project-schema.json or project-package-schema.json:

• Update the examples:
  • docs/examples/example.json
  • docs/examples/blank.json
• Run ./manage.py pre-commit to update docs/_static/i8n.csv

If you added a new definition to the schema, update docs/reference/schema.md:

• Add an entry to the components section
• Update the :collapse: parameter of the jsonschema directive for any schemas or sub-schemas that reference the new definition

If you added a new codelist:

• Add an entry to docs/reference/codelists.md

[duncandewhurst]

Once you've committed my suggestion, you can request a review from James.

[jpmckinney]

One Markdown format issue. Otherwise approved.