[Typescript-Angular] String response not handled correctly

Description

Endpoints that return a string are not handled correctly by the generated Typescript-Angular client. As per https://angular.io/guide/http#requesting-non-json-data if the response type is not json, then a type param should not be provided.

Swagger-codegen version

First identified in 2.3.0, still existing in master.

Command line used for generation

./bin/typescript-angular-petstore-all.sh

Steps to reproduce

1. Run the script and see that in the user.service.ts file, the login method calls return this.httpClient.get<string>(${this.basePath}/user/login``
2. The <string> should not be there

Related issues/PRs

Most similar issue is the same thing but when the spec returns a file type instead of a string.

Suggest a fix/enhancement

I have some code which I will push which removes the <string> if the response type is a string.

Run ./bin/typescript-angular-petstore-all.sh and inspect the generated user.service.ts login method. Trace the Typescript-Angular generator template responsible for the request, then verify that string responses omit the type parameter and that the generated client still handles other response types correctly.