build(deps): bump gatsby from 4.15.2 to 4.19.2 in /docs

Bumps [gatsby](https://github.com/gatsbyjs/gatsby) from 4.15.2 to 4.19.2.
- [Release notes](https://github.com/gatsbyjs/gatsby/releases)
- [Changelog](https://github.com/gatsbyjs/gatsby/blob/master/CHANGELOG.md)
- [Commits](https://github.com/gatsbyjs/gatsby/compare/gatsby@4.15.2...gatsby@4.19.2)

---
updated-dependencies:
- dependency-name: gatsby
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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