chore(client): get unique discovery file and update urls

[chloecarton]

in order to be less restrictive on the url to get the discovery file content, we get the same file independently from the base_url and update the file content with the baseUrl on load.

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.01%. Comparing base (170ba8d) to head (59f9d0b).
Report is 5 commits behind head on master.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #200      +/-   ##
==========================================
+ Coverage   85.81%   86.01%   +0.20%     
==========================================
  Files          16       16              
  Lines         853      851       -2     
  Branches      171      169       -2     
==========================================
  Hits          732      732              
+ Misses         78       77       -1     
+ Partials       43       42       -1     

Flag	Coverage Δ
unittests	86.01% <100.00%> (+0.20%)	⬆️

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Files with missing lines	Coverage Δ
lumapps/api/base_client.py	80.48% <100.00%> (+0.55%)	⬆️
lumapps/api/client.py	95.23% <ø> (ø)

[beroussel]

Otherwise 👌