Add MR db grant job to dbt cheat sheet

Why is this change being made?

This cheat sheet should reflect the most efficient ways to test an MR. The new job to grant access to the MR database should be included.

This MR also moves the image files so that they are easier to manage in-context

Author Checklist

• Provided a concise title for this Merge Request (MR)
• Added a description to this MR explaining the reasons for the proposed change, per say why, not just what
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  • The when to get approval handbook section explains the workflow in more detail
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