Use `fanotify` instead of `inotify` on Linux if available

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## Feature request

**Which Nextcloud Version are you currently using:** 31.0.10 (desktop client: 3.16.4)

**Is your feature request related to a problem? Please describe.**
I ran into the default inotify limit on my Linux system, and had to bump the limit to compensate. See https://blog.mynacol.xyz/en/nextcloud-inotify/. While inotify was blocked due to the limit, the Nextcloud client only synchronized changes after ~1 hour, which was unexpected and interrupting.

**Describe the solution you'd like**
Today I learned that Linux has a newer file/directory monitoring API called [fanotify](https://man7.org/linux/man-pages/man7/fanotify.7.html) that can recursively monitor directories with one monitor. It even supports an ignore mask to exclude some subfolders that are exempted from synchronization.
This can massively decrease memory usage and elegantly prevent the inotify limit issue I faced.

**Describe alternatives you've considered**
Continuing with inotify and bumping the limit when required.

**Additional context**
The fanotify API is only really usable since Linux 5.1. This shouldn't be a major issue, as that version was released in May 2019, and all upstream supported LTS kernels are newer already.