Add bridge with league/flysystem

[yann-eugone]

yokai/batch is working on files for both reading or writing, but it is often required to download the file to be read, or upload the file that was written.
There is currently no "official" way to do such things.

https://github.com/thephpleague/flysystem is the most famous "filesystem abstraction library", it has a wide support of most filesystem types.

What could be done

• A job to copy files, could be used to both download or upload, using filesystem abstraction
• A job to move files, could be used to both download or upload, using filesystem abstraction
• A scheduler to trigger a job whenever a file exists on filesystem

[codecov]

Codecov Report

Merging #61 (bf37543) into 0.x (69b3cf6) will not change coverage.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##                 0.x       #61   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
- Complexity       724       752   +28     
===========================================
  Files            124       127    +3     
  Lines           1846      1939   +93     
===========================================
+ Hits            1846      1939   +93     

Impacted Files	Coverage Δ
src/batch/src/Trigger/Scheduler/ScheduledJob.php	100.00% <ø> (ø)
...rc/batch-league-flysystem/src/Job/CopyFilesJob.php	100.00% <100.00%> (ø)
...rc/batch-league-flysystem/src/Job/MoveFilesJob.php	100.00% <100.00%> (ø)
...gue-flysystem/src/Scheduler/FileFoundScheduler.php	100.00% <100.00%> (ø)

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