Bump @nuxtjs/sitemap from 2.4.0 to 6.1.4 in /src/frontend

Bumps [@nuxtjs/sitemap](https://github.com/nuxt-modules/sitemap) from 2.4.0 to 6.1.4.
- [Release notes](https://github.com/nuxt-modules/sitemap/releases)
- [Commits](nuxt-modules/sitemap@v2.4.0...v6.1.4)

---
updated-dependencies:
- dependency-name: "@nuxtjs/sitemap"
  dependency-type: direct:development
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>