Deployments and scheduling

[caparker]

• New fetcher schema: Core tables for handlers, fetcher_clients, adapters, deployments, and deployment_adapters
• Cron-based scheduling: Custom domain type with validation for cron expressions, enabling pg_cron to trigger
  queue_deployments() every minute
• Queue-based execution: Uses public.fetchlogs as both job queue and audit log with unique keys for idempotency
• Runtime configuration: All scheduling and deployment settings stored in database tables, enabling changes without
  application redeployment
• Temporal offset support: Accommodates data sources that publish with delay