Fix deprecation warnings with RxJS library

[jmacura]

Bug

Describe the bug
Some methods and usage patterns are deprecated in RxJS 7 and will be dropped in RxJS 8. So let's get ready for a future.

Additional context
RxJS 8 is nowhere near yet, but better keep this in mind.

[FilipLeitner]

This seems to be resolved as all forkJoins are refactored. Other than that we use just basic operators or types which are not being deprecated or changed

[jmacura]

This seems to be resolved as all forkJoins are refactored. Other than that we use just basic operators or types which are not being deprecated or changed

Right. This issue was related to forkJoin() and toPromise() patterns. I can't find any deprecated usage any more so closing this issue 👍

btw, there are some first alpha releases of rxjs 8 but still a long road ahead: ReactiveX/rxjs#6367