perf: Optimize /names-and-versions API with lightweight DAO query

[akhilpathivada]

Summary

• Optimize the GET /metadata/workflow/names-and-versions endpoint backend to avoid loading full WorkflowDef objects. Previously, this endpoint called getAllWorkflowDefs() which runs SELECT json_data — reading and deserializing every workflow definition just to extract name, version, and timestamps.
• Add a Postgres-optimized getWorkflowNamesAndVersions() DAO override that queries only SELECT name, version, created_on, modified_on — no json_data TOAST column read, no JSON deserialization.
• Replace HashMap + TreeSet with LinkedHashMap + ArrayList in the service layer, leveraging the pre-sorted data from the DAO to avoid TreeSet rebalancing overhead.
• Add updateTime field to WorkflowDefSummary with gRPC/protobuf compatibility.

Changes

Backend

• MetadataDAO: Added default getWorkflowNamesAndVersions() method — backward-compatible fallback that iterates getAllWorkflowDefs() and constructs WorkflowDefSummary objects
• PostgresMetadataDAO: Optimized override using SELECT name, version, created_on, modified_on FROM meta_workflow_def ORDER BY name, version — no json_data column, no deserialization
• MetadataServiceImpl: Rewritten getWorkflowNamesAndVersions() to call the new DAO method directly and group results using LinkedHashMap + ArrayList instead of HashMap + TreeSet

Model

• WorkflowDefSummary: Added updateTime field with @ProtoField(id = 4)
• workflowdefsummary.proto: Added int64 update_time = 4
• AbstractProtoMapper: Updated toProto() and fromProto() for the new field

Tests

• MetadataServiceTest: Updated mock to use getWorkflowNamesAndVersions() and verify ascending version order with the new ArrayList-based grouping
• PostgresMetadataDAOTest: Integration test for the optimized DAO query

Backward Compatibility

• No database schema changes or migrations
• No existing endpoints modified or removed
• MetadataDAO.getWorkflowNamesAndVersions() is a default method — existing DAO implementations (Redis, MySQL, etc.) continue to work without changes
• New updateTime field in WorkflowDefSummary uses @ProtoField(id = 4) — additive and backward compatible for gRPC/protobuf clients

Test Plan

• ./gradlew spotlessApply passes
• ./gradlew test passes (core, postgres-persistence)
• Verify /metadata/workflow/names-and-versions returns correct data with updateTime
• Verify version dropdown still works correctly on Workbench page
• Verify no regression on Workflow Definition editor pages