add separator-option in paramstore post processor

[ewoelfel]

Hi,

we do have parameters that are named the following way:
/some/service/subSection/config

The existing setup requires application-properties to be subSection/config which do not represent the standard way of accessing properties with structures.

I suggest introducing a separator option helping to resolve this issue.
This way our example would result in subSection.config

Thanks

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (d9d447e) 72.55% compared to head (8437848) 72.58%.
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Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1210      +/-   ##
============================================
+ Coverage     72.55%   72.58%   +0.03%     
- Complexity     1221     1224       +3     
============================================
  Files           198      198              
  Lines          4463     4469       +6     
  Branches        394      395       +1     
============================================
+ Hits           3238     3244       +6     
  Misses         1000     1000              
  Partials        225      225              

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