Update IGP guide with new workday guidance

Why is this change being made?

This MR updates the IGP Guide HB page to include a detailed step-by-step for each part of the IGP now in Workday. Most of the content is the same, with updated mentions of how each section needs to be completed in Workday.

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
• If the changes affect team members, or warrant an announcement in another way, please consider posting an update in #whats-happening-at-gitlab linking to this MR
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