Create Quickselect for Finding the k-th Smallest Element.cpp

[dev-priyanshu15]

adding Quickselect for Finding the k-th Smallest Element.cpp

Description of Change

Checklist

• Added description of change
• Added file name matches File name guidelines
• Added tests and example, test must pass
• Added documentation so that the program is self-explanatory and educational - Doxygen guidelines
• Relevant documentation/comments is changed or added
• PR title follows semantic commit guidelines
• Search previous suggestions before making a new one, as yours may be a duplicate.
• I acknowledge that all my contributions will be made under the project's license.

Notes:

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[github-actions]

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