[out3Plot]: Add option for increased contrast in hillshades

[PaulaSp3]

Add option for increased contrast for hillshade plots.
Default setting: no increased contrast, so the differences in the plots are small:

before (avaKot example):

with changes, default setup (no increased contrast):

with changes, suggested setup ( increased contrast):

[qltysh]

Coverage Impact

⬆️ Merging this pull request will increase total coverage on master by 0.01%.

Modified Files with Diff Coverage (1)

Rating	File	% Diff	Uncovered Line #s
	avaframe/out3Plot/plotUtils.py	100.0%
	Total	100.0%

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