Clarify where to find issues to start contributing

What does this MR do?

We should guide towards the filter of quick win issues combined with seeking community contributions instead of explaining what the label means. The docs were explaining what the labels meant, which is not as useful as guiding people towards an actual list of issues to work on. Decided on guiding them to our most safe list, which is a combination of quick win issues & seeking community contributions Additionally, I don't believe that guiding people to discover what tests to optimize is a path that offers many contributions as this is rather complex. Optimizing existing code is not really a "quick win" and easy to do, increasing the barrier for entry.

Related issues

Author's checklist

• Optional. Consider taking the GitLab Technical Writing Fundamentals course.
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• ~"frontend"
• ~"backend"
• ~"type::bug"
• ~"database"

These labels cause the MR to be added to code verification QA issues.

Reviewer's checklist

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