Update RXJS to match new Angular project rxjs version

[Akxe]

I'm submitting a

• bug
• feature request
• question

What is the current behavior?
This library depends on rxjs v6.x.x.

What is the expected behavior?
Since new Angular projects are created with rxjs v7.4.x, It would be great if this library would either support both, or support the newer of the two.

Please tell us about your environment:

• Mosaic version: 13.1.0
• Browser: all

Other information:
From codebase observations the most notable breaking changes are:

• Observable.toPromise() - Will break this line (type generics): https://github.com/positive-js/mosaic/blob/master/packages/docs/src/app/shared/stackblitz/stackblitz-writer.ts#L196 - firstValueFrom is ideal replacement for that situation

I did not check all of the code...

[lskramarov]

Good question. Will update soon.

[lskramarov]

We want to update dependencies when we update Angular to version 14.