Bump yargs-parser and postcss-cli in /themes/docuapi

Bumps [yargs-parser](https://github.com/yargs/yargs-parser) to 21.1.1 and updates ancestor dependency [postcss-cli](https://github.com/postcss/postcss-cli). These dependencies need to be updated together.


Updates `yargs-parser` from 11.1.1 to 21.1.1
- [Release notes](https://github.com/yargs/yargs-parser/releases)
- [Changelog](https://github.com/yargs/yargs-parser/blob/main/CHANGELOG.md)
- [Commits](yargs/yargs-parser@v11.1.1...yargs-parser-v21.1.1)

Updates `postcss-cli` from 6.1.3 to 10.1.0
- [Release notes](https://github.com/postcss/postcss-cli/releases)
- [Changelog](https://github.com/postcss/postcss-cli/blob/master/CHANGELOG.md)
- [Commits](postcss/postcss-cli@6.1.3...10.1.0)

---
updated-dependencies:
- dependency-name: yargs-parser
  dependency-type: indirect
- dependency-name: postcss-cli
  dependency-type: direct:development
...

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

Author: dependabot[bot]