[Core] Replace legacy OSGi Scheduler (Runnable) with modern Sling Job Consumer

[bkkothari2255]

The current AEM Project Archetype includes a sample scheduled task (SimpleScheduledTask.java) that implements the java.lang.Runnable interface for the OSGi Scheduler. While functional for basic tasks, this approach is considered a "legacy" pattern in modern AEM development, especially for AEM as a Cloud Service and distributed environments.

The AEM community and Adobe best practices now strongly recommend using Sling Jobs (JobConsumer) for background processing.

The existing Runnable implementation has several limitations in a modern AEM architecture:

1. Guaranteed Execution: OSGi Schedulers are in-memory. If an instance restarts during execution, the task is lost. Sling Jobs are JCR-persisted, ensuring they resume after a restart.
2. Distributed Safety: In a clustered environment (multiple Authors/Publishers), a simple OSGi Scheduler can trigger on all nodes simultaneously, leading to race conditions or VersionConflicts. Sling Jobs are "topology-aware" and ensure a job runs only on one designated node (usually the Leader).
3. Observability: Sling Jobs can be monitored, stopped, and restarted via the Sling Jobs console (/system/console/jobs), providing much better visibility than hidden background threads.

Proposed Changes

1. Deprecate/Replace: Remove SimpleScheduledTask.java or update it to follow the Sling Job pattern.
2. Introduce JobConsumer: Add a new sample SimpleJobConsumer.java implementing the JobConsumer interface.
3. Scheduling Logic: Provide an example of how to trigger this job using the JobManager or a ScheduledJob.

[bkkothari2255]

#1331