Make server-side validation supportable in the standard save function

[ns-vpanfilov]

Is your feature request related to a problem? Please describe.
Currently, server-side validation is only supportable using a custom save function (https://marmelab.com/react-admin/Validation.html#schema-validation).

While that approach works, it has the following limitations:

• Some configurations that (e.g. transform property for Create) are ignored
• Building server-side component is more complex that for Create (due to the fact we need to be inside record context), and it is not documented

Describe the solution you'd like
Allow for a configurable parameter that can be passed to Create and Update components that will translate an error and return it to the form as validation results:

const ServerSideValidation = async (e:Error): Promise< undefined | Record<string, {message: string, messageArgs?: any} >> = {

return undefined // no server-side validation errors to be reported

// OR

return {
   user_name: {
      message: 'messages.validation.invalid_chars',
      messageArgs: {'only numbers are allowed}
   }
} // error message to be displayed for 'user_name' field

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.

[djhi]

Can you check whether #7938 solves your issue? It's planned for 4.9.0

[ns-vpanfilov]

it does. thanks