allow shallow (non-recursive) scan when scanning file storage

[Blaok]

When user files are deleted externally on the filesystem, current version of occ files:scan recursively scans the whole folder, which is not necessary. This patch adds a new argument, i.e., occ files:scan --shallow, to allow shallow scan on a certain folder.

[codecov]

Codecov Report

Merging #9526 into master will increase coverage by <.01%.
The diff coverage is 70%.

@@             Coverage Diff             @@
##             master   #9526      +/-   ##
===========================================
+ Coverage      51.7%   51.7%   +<.01%     
  Complexity    25744   25744              
===========================================
  Files          1643    1643              
  Lines         96506   96511       +5     
  Branches       1393    1393              
===========================================
+ Hits          49894   49897       +3     
- Misses        46612   46614       +2

Impacted Files	Coverage Δ	Complexity Δ
lib/private/Files/Utils/Scanner.php	77.11% <100%> (ø)	40 <16> (ø)	⬇️
apps/files/lib/Command/Scan.php	22.04% <62.5%> (+2.15%)	51 <11> (ø)	⬇️
apps/files_trashbin/lib/Expiration.php	90.32% <0%> (-1.62%)	29% <0%> (ø)
apps/files_trashbin/lib/Trashbin.php	72.46% <0%> (-0.25%)	136% <0%> (ø)

[pann]

We are using Nextcloud together with a backup system, but we do not want to generate meta-data for the backup folders as they can be very large and the scan takes very long time.
This patch is implementing just what I need, anything that I can do to help the process?

[MorrisJobke]

Code makes sense 👍 Works here

[MorrisJobke]

@icewind1991 @rullzer Could you have a look?