added new endpoint to get filtered courses according to price and category id

[sumitt-kun]

Issue Title: New Feature: New endpoint to get filtered courses according to price and category id.

resolve issue: #46

I have added a new endpoint to get filtered courses according to price and category id. Please note that if you don't add price in body while making http request then it will return all free courses(i.e price=0). Also if you don't add category id then it will return courses with any category.(i.e no filter on courses will be applied)

Type of change ☑️

What sort of change have you made:

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Code style update (formatting, local variables)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

Checklist: ☑️

• [x] My code follows the guidelines of this project.
• [x] I have performed a self-review of my own code.
• [x] I have commented my code, particularly wherever it was hard to understand.
• [ ] I have made corresponding changes to the documentation.
• [x] My changes generate no new warnings.
• [x] I have added things that prove my fix is effective or that my feature works.
• [x] Any dependent changes have been merged and published in downstream modules.

Screenshot of the changes made in your work (if applicable):

How Has This Been Tested? ⚙️

I've tested it on postman.

[github-actions[bot]]

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[sumitt-kun]

hey @ashutoshgithubs , is it okay if I add the frontend part as a new issue since this is marked just a level 2? Other people are literally just changing little bit of styling/adding just 2-3 lines of code and getting 10 points(for a level 1 issue) :( Please let me know, if its fine. Otherwise I'll add the frontend part in this one only.

[sumitt-kun]

@ashutoshgithubs ?