[ridge-directed-ring-detector] add demo out-of-focus microscopy images

[ridge-directed-ring-detector] add out-of-focus fluorescent particles microscopy for 3d particle tracking

following up on #4847 [WIP] Adding @eldad-a's ridge directed ring detector

https://github.com/scikit-image/scikit-image/pull/4847#issuecomment-862525850

Adding: 5 example images + IPyNB (that was used to extract these from the source file).