Merge branch 'version-2-2' into 'master'

Use dev endpoint

See merge request covid-19/frontend!142

src/environments/environment.prod.ts

 export const environment = {
   production: true,
-  backend: 'https://exbio.wzw.tum.de/covex/api/',
+  backend: 'https://exbio.wzw.tum.de/covex_dev/api/',
 };