feat(toggle): Add clarity around when to use a toggle vs. other components

What does this MR do?

Discussing the proposed design solution for issue gitlab-org/gitlab#328553 (closed) with @mle, resulted in a conversation around the use of Toggle vs Checkbox on the Settings page setting. This MR is an opportunity for the team to take the discussion forward and document a conclusion as a section in the guidelines.

• Removed table comparing the different selection components because it was hard to use
• Add section on When to use a toggle
  • Add comment to consider using a toast for feedback.
  • Add reference to solution validation insight
• Add section When not to use a toggle
  • Add cases beyond needing to submit to consider not using a toggle
  • Add other components as a list instead of a table from before

Does this MR meet the acceptance criteria?

• The MR title and commit message meet the Pajamas commit conventions
• Add a description to this MR explaining the reasons for the proposed change, per say-why-not-just-what
• Include MR scope that reflects the purpose of the change in the description
  • For example, if this MR is focused on usage guidelines, addressing accessibility challenges could be added separately with a different MR
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