[Backend] Limiting the Number of upvotes/downvotes a particular user can do Fixed

[hemanthkumar-21]

Issue that this pull request solves

Issue Link resolve #919 Closes: #919

Brief description of what is fixed or changed

As the Q&A section is open, users can do the upvote and downvotes any umber of times. Now tey can vote only once.

Types of changes

Put an x in the boxes that apply

• [x] Bugfix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Documentation update (Documentation content changed)
• [ ] Other (please describe):

Checklist

Put an x in the boxes that apply

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] My changes generate no new warnings
• [ ] My changes does not break the current system and it passes all the current test cases.