feat: implemented backend api support for keyword-based search mechanism

[cindy-wg]

Implemented a backend change so that the search bar frontend feature (#34) is able to be used to enter a keyword and filter through posts in different categories and pages according to the topic. This is done through an API endpoint that filters through topic titles and keeps ones containing the keyword. The purpose of this is to allow users to search posts by topic based on keywords no matter the page or category they are searching through. Solves #28

Searching 'hello'

Searching 'nodebb'

Seaching 'x' (no results)

[coveralls]

Pull Request Test Coverage Report for Build 13577464713

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

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Details

• 20 of 22 (90.91%) changed or added relevant lines in 5 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.004%) to 82.678%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/api/search.js	5	6	83.33%
src/topics/search.js	10	11	90.91%

Totals
Change from base Build 13575545299:	0.004%
Covered Lines:	22376
Relevant Lines:	25641

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💛 - Coveralls

[nysagarg04]

This is amazing! Great work!

[ethan1696]

Looks good to me!