Bump ajv and ajv-cli in /packages/koa-prometheus

Bumps [ajv](https://github.com/ajv-validator/ajv) to 8.12.0 and updates ancestor dependency [ajv-cli](https://github.com/ajv-validator/ajv-cli). These dependencies need to be updated together.


Updates `ajv` from 3.8.10 to 8.12.0
- [Release notes](https://github.com/ajv-validator/ajv/releases)
- [Commits](https://github.com/ajv-validator/ajv/commits/v8.12.0)

Updates `ajv-cli` from 0.6.0 to 5.0.0
- [Release notes](https://github.com/ajv-validator/ajv-cli/releases)
- [Commits](ajv-validator/ajv-cli@0.6.0...v5.0.0)

---
updated-dependencies:
- dependency-name: ajv
  dependency-type: indirect
- dependency-name: ajv-cli
  dependency-type: direct:development
...

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