Remove deprecated Configuration::getValue ECKIT-648

[marcosbento]

Description

Implement changes requested by https://jira.ecmwf.int/browse/ECKIT-648.

Contributor Declaration

By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.

🌦️ >> Documentation << 🌦️
https://sites.ecmwf.int/docs/dev-section/eckit/pull-requests/PR-249

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 66.22%. Comparing base (842765c) to head (65b637d).
⚠️ Report is 1 commits behind head on release/2.0.0.

Additional details and impacted files

@@                Coverage Diff                @@
##           release/2.0.0     #249      +/-   ##
=================================================
- Coverage          66.24%   66.22%   -0.02%     
=================================================
  Files               1130     1130              
  Lines              57955    57955              
  Branches            4394     4394              
=================================================
- Hits               38393    38382      -11     
- Misses             19562    19573      +11     

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