#446 Add image_face_count_filter and related tests

[TobyJasper]

#446

1. New Operator: image_face_count_filter

• Added the image_face_count_filter operator, which filters images based on the number of faces detected.
• This operator helps users specify images that contain a desired number of faces, ensuring higher accuracy for face-related data processing tasks.

2. Unit Tests:

• Created unit tests for the image_face_count_filter operator to validate its functionality.
• Added a sample test image img8.jpg containing four faces.

3. Updates to StatsKeysConstant:

• Extended the StatsKeysConstant class to include a new constant face_counts, which will store the number of faces detected in an image.

[drcege]

Good!