fix(issue-387): add difficulty filter for challenges

[harireddy7]

Title and Issue number

Title: Add difficulties filter on the challenges screen

Issue No. : #387

Code Stack: host

Close #387

Checklist:

• [x] I have mentioned the issue number in my Pull Request.
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have created a helpful and easy to understand README.md
• [ ] I have updated the Index.html file for my contribution

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