Added Feature to support multiple monitors #766

[Amanullah1002]

What kind of change does this PR introduce?
This PR adds multiple monitor screenshot feature.

Summary
Fixes #766
/claim #766

I have followed the styles guidelines , and commented the code for better understanding.

Checklist

• My code follows the style guidelines of OpenAdapt
• I have performed a self-review of my code
• If applicable, I have added tests to prove my fix is functional/effective
• I have linted my code locally prior to submission
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (e.g. README.md, requirements.txt)
• New and existing unit tests pass locally with my changes

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[abrichr]

Thank you @Amanullah1002 ! Can you please run python -m openadapt.visualize and take some screenshots of the visualization containing more than one monitor?