[Feature][Core] Calculate thresholding confidence using data

[Udayraj123]

The core logic of OMRChecker revolves around finding the correct separation between Marked and Unmarked bubbles. We want to let the user know if it has been determined confidently.

In the above image there are two possible thresholds based on the jumps in the histogram. In such cases the confidence metric will be useful to separate bad quality images.

More references in Rich Visuals section.

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