FDB-624: Update list tool to suport listing (only) duplicates

[simondsmart]

Description

Integration have been trying to identify duplicated data in the output of the IFS suites, without knowing what data
is duplicated in advance. This tool should help them do that.

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 Z3FDB 🚧📖🌦️🌈
https://sites.ecmwf.int/docs/dev-section/z3fdb/pull-requests/PR-217

🌈🌦️📖🚧 Documentation FDB 🚧📖🌦️🌈
https://sites.ecmwf.int/docs/dev-section/fdb/pull-requests/PR-217

[ChrisspyB]

There should be an error if you call the API requesting "duplicates only" AND "deduplication".

[codecov-commenter]

Codecov Report

❌ Patch coverage is 87.50000% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.32%. Comparing base (8abf5d2) to head (6273bc2).

Files with missing lines	Patch %	Lines
src/fdb5/tools/fdb-list.cc	80.95%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #217      +/-   ##
===========================================
+ Coverage    73.30%   73.32%   +0.02%     
===========================================
  Files          363      363              
  Lines        21956    21973      +17     
  Branches      2253     2257       +4     
===========================================
+ Hits         16094    16111      +17     
  Misses        5862     5862              

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