[typescript-fetch] Response headers are not available

[bvwells]

Description

Response headers are not available on generated APIs for the typescript-fetch generator. A similar issue was recently fixed for the typescript-angular generator (#6902).

Swagger-codegen version

2.4.0-SNAPSHOT

Swagger declaration file content or url

https://github.com/swagger-api/swagger-codegen/blob/master/modules/swagger-
codegen/src/test/resources/2_0/petstore.yaml

Command line used for generation

swagger-codegen generate -i modules/swagger-codegen/src/test/resources/2_0/petstore.yaml -l typescript-node -o samples/client/petstore/typescript-node/default"

Steps to reproduce

Related issues/PRs

#6902 for typescript-angular generator

Suggest a fix/enhancement

[macjohnny]

@bvwells thanks for reporting. would you like to give it a try and implement this?

[michalzysk]

+1