Canny auto threshold

[rolalaro]

Added several features:

• a vpImageFilter::median that computes the median of a single- or multi- channel image
• the possibility to ask the automatic computation of the Canny edge detector thresholds
• update of the tutorial accordingly
• update of the tests to test the vpImageFilter::median methods

[codecov]

Codecov Report

Patch coverage: 67.07% and project coverage change: -0.01% ⚠️

Comparison is base (83555f3) 54.98% compared to head (fcf0a43) 54.97%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1213      +/-   ##
==========================================
- Coverage   54.98%   54.97%   -0.01%     
==========================================
  Files         399      399              
  Lines       49201    49252      +51     
==========================================
+ Hits        27051    27075      +24     
- Misses      22150    22177      +27     

Files Changed	Coverage Δ
modules/core/src/image/vpImageFilter.cpp	60.54% <53.44%> (-3.29%)	⬇️
modules/core/include/visp3/core/vpImageFilter.h	92.34% <100.00%> (-0.05%)	⬇️

... and 2 files with indirect coverage changes

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[fspindle]

Ready to merge when ci ok