Fixes #131

This PR adds updateAnnotatedFile property to @OpenApi() annotation.

When the timestamp is forcibly added or updated to the @OpenApi() annotated class, frequent differences occur in source control. Therefore, by adding the updateAnnotatedFile property, if false is set, the addition or update of the timestamp will not be performed.

@Openapi(
  ...
  updateAnnotatedFile: false,
)

Default is true to keep current behavior.

The operation was checked by uncommenting in openapi-generator/pubspec.yaml.

# dependency_overrides:
#  openapi_generator_annotations:
#    path: ../openapi-generator-annotations