Add option to provide custom auth and api url for spring example project

[lojzatran]

I will add the custom auth and api url for other examples later sometimes later. I created a task for it: https://commercetools.atlassian.net/browse/DEVX-495

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 10.06%. Comparing base (48edc67) to head (f370572).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #764   +/-   ##
=========================================
  Coverage     10.06%   10.06%           
  Complexity     1944     1944           
=========================================
  Files          6818     6818           
  Lines         66621    66621           
  Branches        279      279           
=========================================
  Hits           6704     6704           
  Misses        59743    59743           
  Partials        174      174           

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