feat: add a reverse multi option policy

[phlptp]

use it for the default in set_config and simplify and add more flexibility to the the config processing, and potentially in other options as well.

The reverse policy returns a vector but in reversed order from normal. This is what we want in the config processing

Inspired by #862, and updated with recent code changes.

[phlptp]

@VolkerChristian I think this does what you were thinking in #862? I borrowed some code from that PR and added you as a co-author.

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (6da4ff5) 99.46% compared to head (cca6e64) 99.46%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #918   +/-   ##
=======================================
  Coverage   99.46%   99.46%           
=======================================
  Files          18       18           
  Lines        4108     4118   +10     
=======================================
+ Hits         4086     4096   +10     
  Misses         22       22           

Files Changed	Coverage Δ
include/CLI/App.hpp	100.00% <ø> (ø)
include/CLI/Option.hpp	100.00% <ø> (ø)
include/CLI/impl/App_inl.hpp	99.31% <100.00%> (+<0.01%)	⬆️
include/CLI/impl/Option_inl.hpp	99.75% <100.00%> (+<0.01%)	⬆️

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