Bump ajv, @angular-devkit/build-angular and @angular/cli

Bumps [ajv](https://github.com/ajv-validator/ajv) to 6.12.6 and updates ancestor dependencies [ajv](https://github.com/ajv-validator/ajv), [@angular-devkit/build-angular](https://github.com/angular/angular-cli) and [@angular/cli](https://github.com/angular/angular-cli). These dependencies need to be updated together.


Updates `ajv` from 6.10.0 to 6.12.6
- [Release notes](https://github.com/ajv-validator/ajv/releases)
- [Commits](ajv-validator/ajv@v6.10.0...v6.12.6)

Updates `@angular-devkit/build-angular` from 0.802.0 to 15.0.0
- [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/commits/15.0.0)

Updates `@angular/cli` from 8.2.0 to 8.3.29
- [Release notes](https://github.com/angular/angular-cli/releases)
- [Changelog](https://github.com/angular/angular-cli/blob/main/CHANGELOG.md)
- [Commits](angular/angular-cli@v8.2.0...v8.3.29)

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

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

Author: dependabot[bot]