[script][figure] Allows a number of legend > #systems

It is used to define custom legends for dev, eval plots
4 jobs for histlegends in 10 minutes and 11 seconds (queued for 6 seconds)
Status Job ID Name Coverage
  Build
passed #140497
docker
build_linux_27

00:09:16

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passed #140498
docker
build_linux_36

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passed #140499
macosx
build_macosx_27

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passed #140500
macosx
build_macosx_36

00:09:35

86.0%