Add a "pause sync for specific folder" function

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## Feature request

**Which Nextcloud Version are you currently using:** Nextcloud Desktop Client Version 3.17.3 (macOS)

**Is your feature request related to a problem? Please describe.**

I sometimes want to work on a big folder and stop the synchronisation there, but want to keep the synchronisation in other smaller folders. (In my case because I have a .git folder in there).
Other times, I have reduced brandwidth and want to synchronise only one important folder I am working on at the moment, and not synchronise changes made by others.

**Describe the solution you'd like**

The best would be an option "pause sync for specific folder" below the "pause sync for all" button, then one would be able to pick the folder to pause. They would also show with a different icon in the list of synchronised folder.

**Describe alternatives you've considered**

I think being able to choose between synchonise, do not synchronise and pause synchronise option in the list of folder synchronised may be misleading, but may be also a good option if someone can come with a design that works.

**Additional context**

This is related to #1238, #1362