Annotation to exclude some arguments for toString

[AlexDochioiu]

Hello! I think it would be nice to have some kind of argument annotation that would allow us to exclude specific args from toString. Something along the lines of:

@freezed
sealed class PoolMetadata with _$PoolMetadata {
  PoolMetadata._();

  factory PoolMetadata({
    required String metadataUrl,
    required Uint8List metadataHash,
    @OmitToString required CborLengthType cborLengthType,
  }) = _PoolMetadata;
}