Add page about saving settings

What does this MR do?

Add a new page in Pajamas to document the ideal pattern to save settings.

Areas to cover

• Feedback (alerts, toasts)
• Toggles and Feedback
• Save button and copy
• Leaving the page with unsaved changes

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
• If creating a new page on Pajamas from scratch, follow the page template structure
• Follow the Pajamas Voice & Tone Guidelines and GitLab Documentation Style Guide
• Link components to and from other related components and patterns on the .md file, where helpful
• If embedding a Figma file, follow the Figma embed guide
• Assign it to a reviewer. All GitLab designers are reviewers, but you can also assign it directly to a maintainer or trainee maintainer
• Apply the correct component label(s)
• Select a milestone or due date

Links