feat: add datasource schema read methods

[MikeNitsenko]

Check List

• Tests have been run in packages where changes made if available
• Linter has been run for changed code
• Tests for the changes have been added if not covered yet
• Docs have been added / updated if required

[Copilot]

Pull Request Overview

This PR adds new data source metadata query methods to the QueryOrchestrator, enabling retrieval of schemas, tables, and columns through cached query operations.

Key changes:

• Adds three new public methods for querying metadata: queryDataSourceSchemas, queryTablesForSchemas, and queryColumnsForTables
• Implements caching support for metadata operations with configurable refresh options
• Extends QueryCache to handle metadata-specific operations through a new query handler

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
packages/cubejs-query-orchestrator/src/orchestrator/QueryOrchestrator.ts	Adds metadata query methods and operation types with caching support
packages/cubejs-query-orchestrator/src/orchestrator/QueryCache.ts	Implements metadata query handler and cancel handler for the queue system
packages/cubejs-query-orchestrator/test/unit/QueryOrchestrator.test.js	Adds comprehensive test suite covering all metadata methods and integration scenarios