fix(extensions): generate all sub-types that define x-go-type-names (…

…#1397)

In the case that a child type/enum defines `x-go-type-name`s, we don't
currently generate these correctly, therefore we should look at all
`AdditionalTypes` that need adding.

Co-authored-by: Jamie Tanna <jamie.tanna@elastic.co>

internal/test/issues/issue-1397/config.yaml

@@ -0,0 +1,8 @@
+# yaml-language-server: $schema=../../../../configuration-schema.json
+package: issue1397
+generate:
+  echo-server: true
+  client: true
+  models: true
+  embedded-spec: true
+output: issue1397.gen.go

internal/test/issues/issue-1397/doc.go

@@ -0,0 +1,3 @@
+package issue1397
+
+//go:generate go run github.com/deepmap/oapi-codegen/v2/cmd/oapi-codegen --config=config.yaml spec.yaml