[Access] Changed max subscription error code to 429

[Guitarheroua]

In this PR the error code for max subscriptions reached was changed from 503 to 429, as this is not a server error, but more server limitation.

See context here

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 41.24%. Comparing base (89dfb91) to head (56a5991).
Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
engine/access/rest/websockets/controller.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7158   +/-   ##
=======================================
  Coverage   41.24%   41.24%           
=======================================
  Files        2171     2170    -1     
  Lines      190061   190028   -33     
=======================================
- Hits        78391    78384    -7     
+ Misses     105127   105103   -24     
+ Partials     6543     6541    -2     

Flag	Coverage Δ
unittests	41.24% <0.00%> (+<0.01%)	⬆️

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[peterargue]

is there a test case that covers this? If not we should add one.

[illia-malachyn]

is there a test case that covers this? If not we should add one.

Yes, there is. I updated the PR