Draft: Support Learning Pathways: significant redesign, add info on hybrid model

Why is this change being made?

This MR builds on work done in an OKR from FY22, which created the mermaid diagram for the Support hybrid onboarding model, and is part of improvements being put forward together in gitlab-com/support/support-team-meta#4048 (closed).

This MR redesigns the Support Learning Pathways handbook page.

Author Checklist

• Provided a concise title for the MR
• Added a description to this MR explaining the reasons for the proposed change, per say-why-not-just-what
  • Copy/paste the Slack conversation to document it for later, or upload screenshots. Verify that no confidential data is added.
• Assign reviewers for this change to the correct DRI(s)
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to one of the people listed in the "Maintained by" section in on the page being edited.
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• 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.
  • If this is a change that directly impacts the majority of global team members, it should be a candidate for #company-fyi. Please work with internal communications and check the handbook for examples.

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