Bump postcss and @angular-devkit/build-angular in /webapp/frontend

Bumps [postcss](https://github.com/postcss/postcss) to 8.4.31 and updates ancestor dependencies [postcss](https://github.com/postcss/postcss) and [@angular-devkit/build-angular](https://github.com/angular/angular-cli). These dependencies need to be updated together.


Updates `postcss` from 8.4.21 to 8.4.31
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](https://github.com/postcss/postcss/compare/8.4.21...8.4.31)

Updates `postcss` from 8.4.5 to 8.4.31
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](https://github.com/postcss/postcss/compare/8.4.21...8.4.31)

Updates `@angular-devkit/build-angular` from 13.3.11 to 16.2.5
- [Release notes](https://github.com/angular/angular-cli/releases)
- [Changelog](https://github.com/angular/angular-cli/blob/main/CHANGELOG.md)
- [Commits](https://github.com/angular/angular-cli/compare/13.3.11...16.2.5)

---
updated-dependencies:
- dependency-name: postcss
  dependency-type: indirect
- dependency-name: postcss
  dependency-type: indirect
- dependency-name: "@angular-devkit/build-angular"
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>

webapp/frontend/package.json

@@ -47,7 +47,7 @@
         "web-animations-js": "^2.3.2"
     },
     "devDependencies": {
-        "@angular-devkit/build-angular": "v13-lts",
+        "@angular-devkit/build-angular": "v16-lts",
         "@angular/cli": "v13-lts",
         "@angular/compiler-cli": "v13-lts",
         "@angular/language-service": "v13-lts",