Expose `CpsCronValidationService` publicly via an `InjectionToken`

[fateeand]

1. Rename CronValidationService to CpsCronValidationService
2. Move it from cps-ui-kit/src/lib/services/cron-validation.service.ts to cps-ui-kit/src/lib/services/cps-cron-validation/cps-cron-validation.service.ts
3. Create CPS_CRON_VALIDATION_SERVICE injection token, so it can be reimplemented/disabled by consumer apps
4. Inject it to CpsSchedulerComponent
5. Expose it through public-api.ts
6. Add the service API to the Scheduler component page in the composition app