Convert notification actions to a custom preference

[XiangRongLin]

What is it?

• Codebase improvement (dev facing)

Description of the changes in your PR

• Convert NotificationSettingsFragment into a custom Preference
  • extract scale switch out of this
• Create "standard" preference with scale switch and custom preference above

Fixes the following issue(s)

• closes [Codebase] Non standard notification setting layout xml #4646

APK testing

app-debug.zip (updated with Stypox suggestions)

Site notes

• Preference.onDetached() seems to equivalent to Fragment.onPause() for the purpose of saving the preference and recreating the notification.
• From the doc on the 4 constructors of Preference, only modifying the one that i did should be enogh (I think).

Due diligence

• I read the contribution guidelines.

[Stypox]

Thank you! I didn't know this could be done, but it certainly simplifies code ;-)

[XiangRongLin]

Github does have a squash and merge feature right? Otherwise I'm going to squash it manually.

[Stypox]

@XiangRongLin thank you! @TobiGr merge, I already added it in release draft