[Typescript-Angular] Generate client code with rxjs for Angular6+

Description

Feature Request

The client code generated for typescript-angular uses old version of rxjs which is not supported in Angular6+ projects. To make it work you have to manually install rxjs-compat package with npm: npm install rxjs-compat.

Swagger-codegen version

Swagger Hub

Swagger declaration file content or url

Find attached the api definition in yml:

openapi.zip

Code generated with Swagger Hub:

typescript-angular-client-generated.zip

Command line used for generation

Error in ng build:

BUILD ERROR
diary-shit-client-lib/src/lib/api/diary.service.ts(229,1): error TS1005: '}' expected.
../node_modules/rxjs/Observable.d.ts(1,15): error TS2307: Cannot find module 'rxjs-compat/Observable'.
diary-shit-client-lib/src/lib/api/diary.service.ts(19,10): error TS2305: Module '"D:/DANI/vscode/dairy-shit-libs/node_modules/rxjs/Observable"' has no exported member 'Observable'.

Error: diary-shit-client-lib/src/lib/api/diary.service.ts(229,1): error TS1005: '}' expected.
../node_modules/rxjs/Observable.d.ts(1,15): error TS2307: Cannot find module 'rxjs-compat/Observable'.
diary-shit-client-lib/src/lib/api/diary.service.ts(19,10): error TS2305: Module '"D:/DANI/vscode/dairy-shit-libs/node_modules/rxjs/Observable"' has no exported member 'Observable'.

    at Object.<anonymous> (D:\DANI\vscode\dairy-shit-libs\node_modules\ng-packagr\lib\ngc\compile-source-files.js:65:19)
    at Generator.next (<anonymous>)
    at fulfilled (D:\DANI\vscode\dairy-shit-libs\node_modules\ng-packagr\lib\ngc\compile-source-files.js:4:58)
    at <anonymous>

diary-shit-client-lib/src/lib/api/diary.service.ts(229,1): error TS1005: '}' expected.
../node_modules/rxjs/Observable.d.ts(1,15): error TS2307: Cannot find module 'rxjs-compat/Observable'.
diary-shit-client-lib/src/lib/api/diary.service.ts(19,10): error TS2305: Module '"D:/DANI/vscode/dairy-shit-libs/node_modules/rxjs/Observable"' has no exported member 'Observable'.

Steps to reproduce

0. Generate code with Swagger Hub from yml file (see attached)
1. Download generated code for typescript-angular (see attached)
2. Create new angular project with ng-cli and copy generated code
3. Compile with ng build - see errors in console

Suggest a fix/enhancement

Generate the client code with the latest versions of rxjs for Angular6+.

Start by locating the typescript-angular generator templates and the generated imports shown in diary.service.ts, then reproduce the ng build failure using the attached OpenAPI and generated client archives. Done means the generated Angular client builds for Angular 6+ without requiring rxjs-compat and without the reported TypeScript errors.