Support for jsonschema v7 and v2020-12

[RonnyB71]

Description

This ensures that the datamodels backend converts XSD's to JsonSchema 2020-12 format and accepts updates on the same format.

Related Issue(s)

• #8832

Verification

• [x] Your code builds clean without any errors or warnings
• [x] Manual testing done (required)
• [ ] Relevant automated test added (if you find this hard, leave it and we'll help out)
• [x] All tests run green

Documentation

• [ ] User documentation is updated with a separate linked PR in altinn-studio-docs. (if applicable)