[Hivemind] Refactor Github issue extraction functions to object orientated code

[cyri113]

Part of the Github Vectorize (Summary). Please read this document before starting.

This task consists or refactoring a part of the code from functional programming to object-orientated code.

The following changes should be implemented in dags/hivemind_etl_helpers/src/db/github/extract.

Tasks

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1. Create a class GithubIssueExtraction
2. Migrate fetch_raw_issues to a private method _fetch_raw_issues in GithubIssueExtraction
3. Migrate the fetch_issues to a public method fetch_issues in GithubIssueExtraction
4. Make the class GithubExtraction inherit GithubIssueExtraction
5. Update the code base to use the GithubIssueExtraction.fetch_issues instead of the fetch_issues
6. Update the test cases

Note: file coverage should be 100%.

[JacobCWBillings]

Code pushed passed all checks