Resolve "Update to Angular 16"

Closes #6 (closed)

projects/kypo-trainings-clustering-viz-lib/src/lib/visualization/api/visualization-data-default-api.service.ts

-import { HttpClient, HttpHeaders, HttpRequest } from '@angular/common/http';
+import { HttpClient, HttpHeaders } from '@angular/common/http';
 import { Injectable } from '@angular/core';
-import { Observable, of } from 'rxjs';
+import { Observable } from 'rxjs';
 import { map } from 'rxjs/operators';
 import { ConfigService } from '../config/config.service';
 import { VisualizationDataDTO } from '../DTOs/visualization-data-dto';