Add keyword search and testing - Back-end

[aalman3]

In this issue, we will add a feature for filtering in discussions by searching through all questions asked using entered keyword(s). The issue has been split in two sub-issues, issue #42 concerns the back-end code without test code implementation, and issue #43 concerns formal test code being written.

Estimated effort:
The task will require about 2-3 days to complete. Bugs and other issues might take another day to fix. Around 3-4 days in total.

Dependencies among other tasks:
There are no dependencies among other tasks.

Initial assignments for team members:
Initially assigned to Abdallah Almana: @aalman3. Changed to Najoud Al-Talib: @njouud.

Milestones to indicate which sprint the issue should be completed in:
Sprint 1.

Justification for not meeting milestone:
Had to split testing and backend code into separate issues as testing took longer than expected, needed more understanding of the test suite and could not manually test as the front and back end connections were not done.

Acceptance criteria:
This feature will be tested by creating 15 temporary questions in the code and filtering through them using the keyword: "spanish". There will be 5 temporary discussions created using the word spanish. As a student, you will only be able to see the 5 discussions including the word "spanish".