Dynamic sharing for files

[paultranvan]

This adds the possibility to define a permission on a dir_id, which is useful to share a directory through a selector.
Note this only handles one level of a hierarchy: full recursive permissions will probably require more work.

[codecov-io]

Codecov Report

Merging #526 into master will increase coverage by 0.13%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #526      +/-   ##
==========================================
+ Coverage   69.72%   69.85%   +0.13%     
==========================================
  Files         119      119              
  Lines        9870     9873       +3     
==========================================
+ Hits         6882     6897      +15     
+ Misses       2151     2141      -10     
+ Partials      837      835       -2

Impacted Files	Coverage Δ
pkg/vfs/permissions.go	80% <0%> (-2.06%)	⬇️
pkg/workers/sharings/sharing_updates.go	54.87% <0%> (ø)	⬆️
pkg/sharings/send_mails.go	69.47% <0%> (ø)	⬆️
web/sharings/sharings.go	80.69% <0%> (+0.09%)	⬆️
pkg/workers/sharings/share_data.go	74.48% <0%> (+1.37%)	⬆️
pkg/workers/konnectors/konnector.go	70.09% <0%> (+1.86%)	⬆️
pkg/lock/simple_redis.go	74.5% <0%> (+9.8%)	⬆️
pkg/realtime/memtopic.go	100% <0%> (+19.23%)	⬆️

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[nono]

We already have permissions on a directory with all its children, including the recursivity thing

[paultranvan]

@nono Ok I missed that. How can we declare them?

[aenario]

@Gara64 you just need to have the permissions on a folder and it will give permission for all its children. However, you need to use the vfs.Allows instead of permissions.Allow to validate them.