Adding Bournes Potentiometer 3386W 3D model

To speed up integration of your PR, please check the following items as you complete them:

• A screenshot of the model(s) aligned with KiCad footprint(s)
• Source files are contributed on the apropriate location
  • Link to the package3d-source pull request or to the script pull request
• Step model submitted in 1:1 scale
• WRL model submitted in 1:2.54 scale
• 3D model alignment checked against KiCad footprint
• WRL model uses correct material properties
• Geometry check performed on the model

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Link to source file MR: kicad-packages3D-source!414 (merged)