Make datasource editor schema errors human readable

[hotzenklotz]

Detailed Description

Ich no comprende :-(

These schema errors are not helpful at all.

Context

I sometimes need to edit the data-source.json thingy manually from the advanced web UI. It is nice that the there is some validation... however the error message as abysmal. Rather then telling me it is not valid, it should me tell either what property is missing or which property value is invalid.

• Specific to long-running jobs (set jobsEnabled=true in application.conf)
• Specific to webKnossos.org (set isDemoInstance=true in application.conf)

[philippotto]

The json schema validation library that we use is responsible for this and can't do much better afaik.

I looked for alternatives and zod seems to have discriminated unions which is exactly what we'd need here.
https://zod.dev/?id=discriminated-unions

To make use of this validation library, it would probably make sense to also switch the form management from antd (which is often quite cumbersome anyway) to something like react-hook-form. Luckily, RHF also supports zod for validation. So, these two libraries should pair up quite nicely.

/edit: To be clear, the validation library could be switched without changing the form library. Both changes make sense in my opinion, but they can be tackled separately.