Add algorithm template forge JSON

[chrisvanrun]

MVP for using future algorithm template forging in grand-challenge-forge.

Part of the pitch:

• https://github.com/DIAGNijmegen/rse-roadmap/issues/338

It adds:

• An algorithm-template context generator for future forging
• A site admin readable field for Algorithm for debugging integration with forge
• Adds example values to the context of the challenge json for the forge