build(deps): bump gatsby-plugin-sitemap from 4.10.0 to 5.0.0 in /docs

Bumps [gatsby-plugin-sitemap](https://github.com/gatsbyjs/gatsby/tree/HEAD/packages/gatsby-plugin-sitemap) from 4.10.0 to 5.0.0.
- [Release notes](https://github.com/gatsbyjs/gatsby/releases)
- [Changelog](https://github.com/gatsbyjs/gatsby/blob/gatsby-plugin-sitemap@5.0.0/packages/gatsby-plugin-sitemap/CHANGELOG.md)
- [Commits](https://github.com/gatsbyjs/gatsby/commits/gatsby-plugin-sitemap@5.0.0/packages/gatsby-plugin-sitemap)

---
updated-dependencies:
- dependency-name: gatsby-plugin-sitemap
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

docs/package.json

@@ -25,7 +25,7 @@
  "gatsby-plugin-react-svg": "^3.1.0",
  "gatsby-plugin-robots-txt": "^1.6.10",
  "gatsby-plugin-sharp": "^3.10.2",
- "gatsby-plugin-sitemap": "^4.10.0",
+ "gatsby-plugin-sitemap": "^5.0.0",
  "gatsby-remark-autolink-headers": "^2.11.0",
  "gatsby-remark-copy-linked-files": "^4.11.0",
  "gatsby-remark-embedder": "^4.2.0",