Bump dompurify and redoc-cli in /docs_src

Removes [dompurify](https://github.com/cure53/DOMPurify). It's no longer used after updating ancestor dependency [redoc-cli](https://github.com/Redocly/redoc). These dependencies need to be updated together.


Removes `dompurify`

Updates `redoc-cli` from 0.13.10 to 0.13.21
- [Release notes](https://github.com/Redocly/redoc/releases)
- [Changelog](https://github.com/Redocly/redoc/blob/main/CHANGELOG.md)
- [Commits](https://github.com/Redocly/redoc/commits)

---
updated-dependencies:
- dependency-name: dompurify
  dependency-type: indirect
- dependency-name: redoc-cli
  dependency-type: direct:production
...

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