docs: adding field descriptions to predefined point cloud 3D document

[punndcoder28]

• Add Field Description and examples to predefined PointCloud3D document Add Field Description and example to Predefined Documents #1736

[punndcoder28]

@JoanFM This PR addresses the changes to add field descriptions and examples for PointCloud3D document

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -1.90% ⚠️

Comparison is base (4ef4939) 81.60% compared to head (9235dbd) 79.70%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1792      +/-   ##
==========================================
- Coverage   81.60%   79.70%   -1.90%     
==========================================
  Files         136      136              
  Lines        9044     9045       +1     
==========================================
- Hits         7380     7209     -171     
- Misses       1664     1836     +172     

Flag	Coverage Δ
docarray	79.70% <100.00%> (-1.90%)	⬇️

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

Files Changed	Coverage Δ
docarray/documents/point_cloud/point_cloud_3d.py	92.30% <100.00%> (+0.30%)	⬆️

... and 5 files with indirect coverage changes

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