Add granularity parameter to control segmented object size

[HendricksJudy]

Fixes #770

Add granularity parameter to control segmented object granularity.

• segment_anything/automatic_mask_generator.py

  • Add granularity parameter to SamAutomaticMaskGenerator class constructor.
  • Update generate method to blend smaller segments into larger ones based on the granularity parameter.
  • Add blend_segments method to handle the blending logic based on the granularity parameter.

• scripts/amg.py

  • Add --granularity command-line argument to set the granularity of segmented objects.
  • Pass the granularity argument to the SamAutomaticMaskGenerator class.

• README.md

  • Update documentation to include information about the new granularity parameter.
  • Add examples of how to use the granularity parameter in the Getting Started section.