Bump webpack-dev-middleware and @docusaurus/core

Bumps [webpack-dev-middleware](https://github.com/webpack/webpack-dev-middleware) to 5.3.4 and updates ancestor dependency [@docusaurus/core](https://github.com/facebook/docusaurus/tree/HEAD/packages/docusaurus). These dependencies need to be updated together.


Updates `webpack-dev-middleware` from 3.7.3 to 5.3.4
- [Release notes](https://github.com/webpack/webpack-dev-middleware/releases)
- [Changelog](https://github.com/webpack/webpack-dev-middleware/blob/v5.3.4/CHANGELOG.md)
- [Commits](webpack/webpack-dev-middleware@v3.7.3...v5.3.4)

Updates `@docusaurus/core` from 2.0.0-beta.ff31de0ff to 2.4.3
- [Release notes](https://github.com/facebook/docusaurus/releases)
- [Changelog](https://github.com/facebook/docusaurus/blob/main/CHANGELOG.md)
- [Commits](https://github.com/facebook/docusaurus/commits/v2.4.3/packages/docusaurus)

---
updated-dependencies:
- dependency-name: webpack-dev-middleware
  dependency-type: indirect
- dependency-name: "@docusaurus/core"
  dependency-type: direct:production
...

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