Add ability to customize default Parse Errors

New Feature / Enhancement Checklist

• I am not disclosing a vulnerability.
• I am not just asking a question.
• I have searched through existing issues.

Current Limitation

Sometimes, it would be good to customize the internal errors caused by Parse Server.

Feature / Enhancement Description

It would be good to have a Cloud Function where we could register Parse.Cloud.onError(className, (error) => {}); where the error can be customized before returning to the client.

Example Use Case

An example of this is if you have mongodb unique schemas set up. Let's say you have the fields "foo" to be unique on the class "Test". If a duplicate "foo" value is presented, the error will be "A duplicate value for a field with unique values was provided" which is often useless to clients. It would be good to be able to do:

Parse.Cloud.onError("Test", (error) => {
  if (error.code === Parse.Error.DUPLICATE_VALUE) {
    error.message = 'Foo has already been used. Please try a different one';
  }
});

Alternatives / Workarounds

Use enableExpressErrorHandler

3rd Party References

https://community.parseplatform.org/t/server-wide-custom-error-messages/255

Start with the proposed Parse.Cloud.onError entry point and the enableExpressErrorHandler workaround described in the issue. Clarify the callback lifecycle, supported error scope, and response behavior; done should allow internal errors such as duplicate-value errors to be customized before returning to the client.