Add unbounded_knapsack.py

[kenzonobre]

Describe your change:

Add unbounded knapsack algorithm, which is an extension of the 0-1 knapsack problem.

0-1 Knapsack Problem : https://en.wikipedia.org/wiki/Knapsack_problem https://www.geeksforgeeks.org/0-1-knapsack-problem-dp-10/

Unbounded knapsack : https://www.geeksforgeeks.org/unbounded-knapsack-repetition-items-allowed/

• [X] Add an algorithm?
• [ ] Fix a bug or typo in an existing algorithm?
• [ ] Documentation change?

Checklist:

• [X] I have read CONTRIBUTING.md.
• [X] This pull request is all my own work -- I have not plagiarized.
• [X] I know that pull requests will not be merged if they fail the automated tests.
• [X] This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• [X] All new Python files are placed inside an existing directory.
• [X] All filenames are in all lowercase characters with no spaces or dashes.
• [X] All functions and variable names follow Python naming conventions.
• [X] All function parameters and return values are annotated with Python type hints.
• [X] All functions have doctests that pass the automated testing.
• [X] All new algorithms include at least one URL that points to Wikipedia or another similar explanation.
• [X] If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

[kenzonobre]

@cclauss could you please review my code? I could work on it more if necessary, but I think it looks good

[kenzonobre]

@cclauss could you please review my code? I could work on it more if necessary, but I think it looks good