General improvement to Environment Variables access

[marcosbento]

• Concentrate the Environment Variables under a single API specified at ecflow/core/Environment.hpp
• Replace all raw calls to ::getenv()

Re ECFLOW-1957

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 83.43023% with 57 lines in your changes missing coverage. Please review.

Project coverage is 47.12%. Comparing base (b7e9139) to head (fca83b6).
Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
libs/client/test/SCPort.cpp	43.75%	9 Missing ⚠️
libs/test/src/TestFixture.cpp	0.00%	7 Missing ⚠️
libs/client/test/TestSinglePerf.cpp	0.00%	5 Missing ⚠️
libs/test/TestClkSync.cpp	0.00%	5 Missing ⚠️
libs/base/src/ecflow/base/cts/user/CFileCmd.cpp	50.00%	4 Missing ⚠️
...ibs/client/src/ecflow/client/ClientEnvironment.cpp	82.35%	3 Missing ⚠️
libs/node/src/ecflow/node/JobCreationCtrl.cpp	40.00%	3 Missing ⚠️
libs/node/src/ecflow/node/Submittable.cpp	83.33%	3 Missing ⚠️
libs/core/src/ecflow/core/Environment.hpp	92.59%	2 Missing ⚠️
libs/node/test/TestEcfFile.cpp	95.65%	2 Missing ⚠️
... and 12 more

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #123      +/-   ##
===========================================
- Coverage    47.15%   47.12%   -0.03%     
===========================================
  Files         1181     1182       +1     
  Lines        93472    93344     -128     
  Branches     14736    14706      -30     
===========================================
- Hits         44078    43992      -86     
+ Misses       49394    49352      -42     

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