Add queue for downloader to limit concurrent requests

[akondas]

No description provided.

[codecov]

Codecov Report

Merging #253 into master will increase coverage by 0.13%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master     #253      +/-   ##
============================================
+ Coverage     99.68%   99.81%   +0.13%     
  Complexity     1522     1522              
============================================
  Files           251      251              
  Lines          4432     4434       +2     
============================================
+ Hits           4418     4426       +8     
+ Misses           14        8       -6     

Impacted Files	Coverage Δ	Complexity Δ
src/Service/Downloader/ReactDownloader.php	97.72% <100.00%> (+14.39%)	15.00 <0.00> (ø)

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