Bump http-proxy-middleware and webpack-dev-server in /legacy

Bumps [http-proxy-middleware](https://github.com/chimurai/http-proxy-middleware) to 2.0.7 and updates ancestor dependency [webpack-dev-server](https://github.com/webpack/webpack-dev-server). These dependencies need to be updated together.


Updates `http-proxy-middleware` from 0.19.1 to 2.0.7
- [Release notes](https://github.com/chimurai/http-proxy-middleware/releases)
- [Changelog](https://github.com/chimurai/http-proxy-middleware/blob/v2.0.7/CHANGELOG.md)
- [Commits](chimurai/http-proxy-middleware@v0.19.1...v2.0.7)

Updates `webpack-dev-server` from 3.1.11 to 5.1.0
- [Release notes](https://github.com/webpack/webpack-dev-server/releases)
- [Changelog](https://github.com/webpack/webpack-dev-server/blob/master/CHANGELOG.md)
- [Commits](webpack/webpack-dev-server@v3.1.11...v5.1.0)

---
updated-dependencies:
- dependency-name: http-proxy-middleware
  dependency-type: indirect
- dependency-name: webpack-dev-server
  dependency-type: direct:development
...

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