Allow to tap "Update all channels" while feeds are being auto-updated

[GfEW]

Checklist (fulfilled)

• I made sure that there are no existing issues - open or closed - which I could contribute my information to.
• I have read the FAQ and my problem isn't listed.
• I'm aware that this is a request for NewPipe itself and that requests for adding a new service need to be made at NewPipeExtractor.
• I have taken the time to fill in all the required details. I understand that the feature request will be dismissed otherwise.
• This issue contains only one feature request.
• I have read and understood the contribution guidelines.

Note:

I'm not fully aware of the exact official terminology ("feeds" vs. "channels" etc.), hope you get my point, regardless. Should any confusion arise, please let me know so I can clarify.

Feature description

In the "What's New" tab, while "get notified"-enabled feeds are being auto-updated, keep showing the update info bar and, most importantly, the circular arrow, so if the user, also wants to update all channels, can tap that circular arrow right away.

Why do you want this feature?

When NewPipe is started after some pause with the tab "What's New" selected, notification-enabled feeds are auto-updated correctly. However, depending on their count (and phone specs, network etc.), this procedure can take quite some time.

As of 0.27.x, whenever users then also want to update all channels, they have to wait twice:

1. once for the circular arrow in the upper right corner to reappear (when auto-updates are finished), then tap it, and
2. then again for the update-all triggered in 1. to finish.

This FR asks for a one-time effort to spare users that recurring effort of waiting twice.
The idea is: Whenever you start NewPipe and at that time, also want to update all channels, tap "update-all" right away, then sit down and let the app do all the updates, so you have to wait only once for them to finish (with no need to check or interact meanwhile).

Additional information

• Please refrain from a mere fixed setting like "update all channels upon app start" - or provide it only additionally -, because the choice between "always" and "never" would only trade one nuisance for another, preventing the user from starting NewPipe without updating all channels (think of expensive or slow connections, or when you're only quickly interested in a particular video you got notified about).
• The point of this FR is not to make the circular arrow actually update all channels immediately while auto-updates are still running, but instead, to queue the "update all" request so it's executed as soon as auto-updating is finished.