Update documentation, focusing on how instance-level and project-level interact, in regards to precedence

Overview

With the addition of a project-level toggle for pre-receive secret detection, we will need to update the docs to show how to use it and how it works with the instance level toggle.

Implementation Plan

• Ensure proper wording on new/updated screens
• Update documentation, including screenshots, as necessary

Refinement Progress

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• This issue describes a problem to solve, or a task to complete, and it's confirmed.
• This issue describes a proposal or an implementation plan that outlines a way to solve the problem or complete the task.
• This issue is the smallest iteration possible and doesn't require further break down.
• This issue has weight set - based on how many tasks or merge requests are required - and needs weight label is removed.
• This issue is labeled correctly.
• This issue is reviewed by another team member to confirm strategy and estimate.
• Finally, add workflowready for development label to this issue.