Preparing a 0.4.0 release

[ml-evs]

We are aiming for a release next week or the following week.

PRs to get in first:

• Add "equipment" item type #531
• Convert Whinchat to use langchain  #661
• Allow starting materials and equipment to be edited by normal users #672
• Serve data about available block types in API #667 (if it goes smoothly)

Issues it would be good to tackle:

• Free text search could be improved #679
• Versioning scheme #234 (but specifically for the database, to allow easier migrations in the future)
• Scan through various issues in the 0.3.x and 0.2.x milestones that have been left behind

General things to do:

• Write a good changelog, ideally with GIFs of new UI features
• Do a proper pass on the documentation, including
  • Instructions/tips for updating a deployment
  • Add instructions and links to the Python API
• Expand README note on contributors (not sure if we want to have an explicit list or just link to the GitHub contributors and thank others for testing more generally)
• Check for any urgent dependency updates
• Update version numbers