docs: Add a story demoing height-after-fetch

[smockle]

Follow-up to #1287. From that PR’s description:

Sidebar: The asynchronously-fetch case is partially-supported [Ed: It is—in fact—fully-supported]: A component consumer can initially (before items have been retrieved) pass height="auto" then (once items are retrieved) pass height="initial". Because heightKey is a dependency of the useEffect, the height-after-fetch can be set using this approach.

This PR adds a story demonstrating this pattern.

https://github.com/github/primer/issues/161 described two cases:

1. A SelectPanel whose Items are known during the initial render
2. A SelectPanel whose Items are asynchronously fetched

This story demonstrates that the Overlay component supports content-matched height in both cases (regardless of whether the content is initially available or fetched), so https://github.com/github/primer/issues/161 can considered addressed. Fixes https://github.com/github/primer/issues/161.

Screen recording

Merge checklist

• Added/updated tests
• Added/updated documentation
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge

[changeset-bot]

⚠️ No Changeset found

Latest commit: f73b323

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

[vercel]

This pull request is being automatically deployed with Vercel (learn more).
To see the status of your deployment, click below or on the icon next to each commit.

🔍 Inspect: https://vercel.com/primer/primer-components/Fuuvnvd8mQqnGP7bcYEigndAuccx
✅ Preview: https://primer-components-git-height-after-fetch-primer.vercel.app

[bscofield]

🎉