Add tag description option to exiv2 app

[postscript-dev]

• Add ::tagDesc() to (Exif | Xmp | Iptc) Datums and Keys
• Add --Print d option to exiv2 application
• Update testing
• Update manpage

[codecov]

Codecov Report

Merging #2279 (c92c601) into main (2c31430) will increase coverage by 0.03%.
The diff coverage is 71.42%.

@@            Coverage Diff             @@
##             main    #2279      +/-   ##
==========================================
+ Coverage   63.48%   63.52%   +0.03%     
==========================================
  Files         118      118              
  Lines       19595    19600       +5     
  Branches     9557     9560       +3     
==========================================
+ Hits        12440    12450      +10     
+ Misses       5091     5082       -9     
- Partials     2064     2068       +4     

Impacted Files	Coverage Δ
app/exiv2app.hpp	100.00% <ø> (ø)
include/exiv2/datasets.hpp	100.00% <ø> (ø)
include/exiv2/exif.hpp	100.00% <ø> (ø)
include/exiv2/iptc.hpp	100.00% <ø> (ø)
include/exiv2/metadatum.hpp	76.92% <ø> (ø)
include/exiv2/properties.hpp	100.00% <ø> (ø)
include/exiv2/tags.hpp	33.33% <ø> (-66.67%)	⬇️
include/exiv2/xmp_exiv2.hpp	89.47% <ø> (-1.01%)	⬇️
src/exif.cpp	65.81% <50.00%> (-0.11%)	⬇️
src/iptc.cpp	64.17% <50.00%> (+0.64%)	⬆️
... and 35 more

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