[Bug]: TCGC would return customized error model by default

[MaryGao]

Describe the bug

See playground we have customized error model defined ResponseError.

import "@typespec/rest";

@error
model ResponseError {
  code: int32;
  meesage: string;
}

op test(): void | ResponseError;

Currently it is always returning this error model in TCGC during getAllModels but please note if this error model is defined in azure core, by default we will not return that model. I think it's better to have an option to opt in if we need this model and by default not returning this like azure error model.

Reproduction

NA

Checklist

• Follow our Code of Conduct
• Check that this issue is about the Azure libraries for typespec. For bug in the typespec language or core libraries file it in the TypeSpec repo
• Check that there isn't already an issue that request the same bug to avoid creating a duplicate.
• The provided reproduction is a minimal reproducible example of the bug.