Attach schema to JSON field and validate data by it on save

[MurzNN]

JSON fields are cool, but they are too nonrestrictive! So there are big changes to save non-valid JSON. To solve this problem will be good to implement JSON Schema support (attaching schema to field) and validation by it on backend. Yes, we can make this via custom code, but will be good to have it in core.

[bladey]

Thanks for the feature suggestion @MurzNN!

[MurzNN]

Having schema, we even can improve rendering of edit form in Admin UI, to convert simple plaintext textarea to multiple inputs of several types (string, number, array of strings, etc).

[raveling]

@MurzNN we provided an answer to this question in the recent Q&A event:
https://www.youtube.com/watch?v=r1IJh-iHm1c&t=1085s