More form constraints

[samuelcolvin]

Currently we don't apply many common constraints from pydantic/json schema to forms:

• max length / min length
• gt, lt, ge, le
• multiple of

Shouldn't be too hard to add these to the form field pydantic models, populate them in json_schema.py and add them to the input in the frontend.

[WolfDWyc]

As far as I understand, these can all be validated - but currently only on the server side? I assume the benefit of also validating this client side is speed but I'm not sure if I'm missing any others.

[samuelcolvin]

Yes