chore: add archived notice to docs site

[pfulton]

Description

Adds a site-wide banner to alert users that the docs have been archived and if they wish to contribute, they should refer to the SWC contribution guide.

How and where has this been tested?

Please tag yourself on the tests you've marked complete to confirm the tests have been run by someone other than the author.

Validation steps

Regression testing

Validate:

1. The documentation pages for at least two other components are still loading, including:

• The pages render correctly, are accessible, and are responsive.

2. If components have been modified, VRTs have been run on this branch:

• VRTs have been run and looked at.
• Any VRT changes have been accepted (by reviewer and/or PR author), or there are no changes.

Screenshots

To-do list

• I have read the contribution guidelines.
• I have updated relevant storybook stories and templates.
• I have tested these changes in Windows High Contrast mode.
• If my change impacts other components, I have tested to make sure they don't break.
• If my change impacts documentation, I have updated the documentation accordingly.
• ✨ This pull request is ready to merge. ✨

[changeset-bot]

⚠️ No Changeset found

Latest commit: 4484a75

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

[github-actions]

📚 Branch preview

PR #4351 has been deployed to Azure Blob Storage: https://spectrumcss.z13.web.core.windows.net/pr-4351/index.html.

[github-actions]

File metrics

Summary

Total size: 2.25 MB^*

🎉 No changes detected in any packages

* Size is the sum of all main files for packages in the library.
* An ASCII character in UTF-8 is 8 bits or 1 byte.