feat: add IoTDB datasource support

[HTHou]

Summary

• add IoTDB as a built-in timeseries datasource and register its cache/router wiring
• implement IoTDB table-model metadata/query support and filter system databases from schema discovery
• fix embedded explorer behavior for IoTDB, including datasource routing and chart time normalization

Testing

• go build ./dskit/iotdb ./datasource/iotdb ./center/router ./dscache
• npm run build (in the separate frontend workspace used to regenerate embedded assets)

Notes

• the frontend source lives in a sibling workspace, so the repository-side change updates the embedded frontend assets consumed by this repo
• the corresponding frontend PR is Add standalone IoTDB frontend support n9e/fe#2078