chore(deps): bump katex and rehype-katex in /docs

Bumps [katex](https://github.com/KaTeX/KaTeX) to 0.16.21 and updates ancestor dependency [rehype-katex](https://github.com/remarkjs/remark-math). These dependencies need to be updated together.


Updates `katex` from 0.13.24 to 0.16.21
- [Release notes](https://github.com/KaTeX/KaTeX/releases)
- [Changelog](https://github.com/KaTeX/KaTeX/blob/main/CHANGELOG.md)
- [Commits](KaTeX/KaTeX@v0.13.24...v0.16.21)

Updates `rehype-katex` from 5.0.0 to 7.0.1
- [Release notes](https://github.com/remarkjs/remark-math/releases)
- [Commits](https://github.com/remarkjs/remark-math/compare/[email protected]@7.0.1)

---
updated-dependencies:
- dependency-name: katex
  dependency-type: indirect
- dependency-name: rehype-katex
  dependency-type: direct:production
...

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