[Feat] Add PointCloud Segmentation

[tchaton]

What does this PR do?

This PR adds a PointCloudSegmentation task

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[codecov]

Codecov Report

Merging #566 (803ab59) into master (a340464) will decrease coverage by 1.07%.
The diff coverage is 73.19%.

@@            Coverage Diff             @@
##           master     #566      +/-   ##
==========================================
- Coverage   91.71%   90.63%   -1.08%     
==========================================
  Files         122      132      +10     
  Lines        7327     7766     +439     
==========================================
+ Hits         6720     7039     +319     
- Misses        607      727     +120     

Flag	Coverage Δ
unittests	90.63% <73.19%> (-1.08%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
flash/pointcloud/segmentation/open3d_ml/app.py	32.00% <32.00%> (ø)
flash/pointcloud/segmentation/datasets.py	50.00% <50.00%> (ø)
...ash/pointcloud/segmentation/open3d_ml/backbones.py	61.70% <61.70%> (ø)
flash/pointcloud/segmentation/model.py	76.66% <76.66%> (ø)
flash/pointcloud/segmentation/data.py	80.00% <80.00%> (ø)
...tcloud/segmentation/open3d_ml/sequences_dataset.py	82.56% <82.56%> (ø)
flash/core/model.py	86.25% <83.78%> (-0.28%)	⬇️
flash/core/data/batch.py	95.85% <100.00%> (-0.58%)	⬇️
flash/core/data/data_module.py	94.35% <100.00%> (+0.41%)	⬆️
flash/core/data/process.py	86.58% <100.00%> (+0.23%)	⬆️
... and 17 more

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[ethanwharris]

Awesome, LGTM 😃