TransformJSONProtoToDSL fails for models with direct assignments

TransformJSONProtoToDSL can fail when given an AuthorizationModel produced by TransformModuleFilesToModel, even though the
model represents valid DSL.

reproduce

user := `
  module user

  type user
  `

group := `
  module group

  type group
    relations
      define member: [user]
  `

  model, err := transformer.TransformModuleFilesToModel([]transformer.ModuleFile{
      {Name: "user.fga", Contents: user},
      {Name: "group.fga", Contents: group},
  }, "1.2")
  if err != nil {
      panic(err)
  }

  _, err = transformer.TransformJSONProtoToDSL(
      model,
      transformer.WithIncludeSourceInformation(true),
  )

my expectation was that this would return the full compiled DSL model, similar to the output of the FGA cli fga model transform

but it fails with

the 'member' relation definition under the 'group' type is not supported by the OpenFGA DSL syntax yet

Start with TransformModuleFilesToModel and TransformJSONProtoToDSL, using the provided user and group module inputs to reproduce the failure. Trace handling of the direct assignment in the group member relation; done means the transformation returns the full compiled DSL model without the unsupported-syntax error.