feat(Accordion): expand usage guidelines

What does this MR do?

The Accordion guidelines are missing some use cases for when to not use the component.

Research shows that forcing users to click on headings one at a time to display full content can be cumbersome and it increases cognitive load. For example, in the Environments and Settings pages, the accordion pattern hides important information from users, diminishing awareness of it.

Accordions are more suitable when users need only a few key pieces of content on a single page. This MR expands the usage guidelines to help designers know when to apply this pattern on their designs.

Does this MR meet the acceptance criteria?

• The MR title and commit messages meet the Pajamas commit conventions.
• The “What does this MR do?” section in the MR description is filled out, explaining the reasons for and scope of the proposed changes, per “Say why not just what”.
  • For example, if the MR is focused on usage guidelines, addressing accessibility challenges could be added in a separate MR.
• Relevant label(s) are applied to the MR.
• The MR is added to a milestone.
• If creating a new component page from scratch, it follows the page template structure.
• Content follows the Pajamas voice and tone guidelines, falling back on the GitLab Documentation Style Guide when needed.
• Related pages are cross-linked, where helpful. Component pages have related components and patterns defined in their Markdown front matter.
• If embedding a Figma file, it follows the Figma embed guide.
• Review requested from any GitLab designer or directly from a maintainer or trainee maintainer.

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