Enhanced query capabilities on workflow instances

[camcima]

Summary

Currently findByUuid and findExpired are the only query methods. In practice, teams need richer querying such as "find all instances of workflow X in state Y" or "find all instances with metadata.orderId = Z".

Proposal

Add query capabilities for workflow instances. Options include:

• findByWorkflowAndState(workflowName, state) — find all instances in a given state
• findByMetadata(key, value) — query by metadata fields (leveraging PostgreSQL JSONB indexing)
• A lightweight query builder for composable filters
• Pagination support for large result sets

Benefits

• Enables operational dashboards and admin tooling
• Supports business queries like "show all orders stuck in payment_pending"
• Leverages PostgreSQL's JSONB indexing capabilities for metadata queries
• Common requirement for production workflow systems

Considerations

• Query performance and indexing strategy (GIN indexes on JSONB columns)
• Whether to expose raw SQL or provide a typed query API
• Pagination and cursor-based iteration for large result sets
• Whether to support ordering (by creation date, last transition, etc.)