feat: add unbounded knapsack algorithm

[mrmagic2020]

Add unbounded knapsack algorithm, class dynamic_programming::unbounded_knapsack. Documentation and test cases included.

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:

[mrmagic2020]

@realstealthninja could you please review or dont-close? Thanks a lot!