feat(Usability): add page for progressive disclosure

What does this MR do?

Adds a page about progressive disclosure.

Problem: in the settings, there are often long forms on top of small tabular layouts. This makes the settings page very long and overwhelming. This MR proposes that long forms whose results display in a list/table should be filled out in a modal or new page. That significantly reduces the amount of information the user has to parse on the settings page.

I've addressed this by adding a page about progressive disclosure that solves this problem but will also be relevant for other areas of the product.

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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