Refactor content style guide updates page

[Chris Pymm (chrispymm)]

The style guide updates page required authoring in html - ading all content manually into a <table> and ensuring all govuk and sortable table classes were correct.

This was hard to do and error-prone, and turned what should be simple content additions into a complex dev-focused task.

This PR extracts all the markup into a layout file, and then makes each style guide update entry into its own .md file which are then collated into an eleventy collection to be output on the style guide updates page within the sortable table layout.

Adding an entry to the style guide is now a matter of creating a new file YYYY-MM-DD-Filename.md within the 'docs/style-guide-updates` directory with the format:

---
title: Entry title
anchor: the anchor link to the item in the style guide (the bit after the #)
type: updated | new
date: yyyy-mm-dd
---

Update content in markdown format

[github-actions]

🚀 Deployed to preview environment! If this is the first deploy, you may have to wait a few minutes for your preview site to be ready on the following URL:

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[github-actions]

🚀 Deployed to preview environment! If this is the first deploy, you may have to wait a few minutes for your preview site to be ready on the following URL:

https://moj-frontend-pr-1722.apps.live.cloud-platform.service.justice.gov.uk

Username: preview, Password: moj

[github-actions]

🚀 Deployed to preview environment! If this is the first deploy, you may have to wait a few minutes for your preview site to be ready on the following URL:

https://moj-frontend-pr-1722.apps.live.cloud-platform.service.justice.gov.uk

Username: preview, Password: moj

[Chris Pymm (chrispymm)]

🎉 This PR is included in version 5.2.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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