[spark] Extend get_cluster_configs procedure output with default value, is_default and description columns

[XuQianJin-Stars]

Purpose

Linked issue: close #xxx

Extend the sys.get_cluster_configs Spark procedure output so users can inspect not only the current value and source of each cluster config, but also its declared default value, whether the current value equals the default, and a human-readable description. This makes the procedure far more useful for diagnostics and onboarding.

Brief change log

• Extended GetClusterConfigsProcedure output schema from 3 columns to 6 columns:
  • config_key (String)
  • config_value (String)
  • config_source (String: DYNAMIC / STATIC / DEFAULT)
  • default_value (String, nullable)
  • is_default (Boolean)
  • description (String, nullable)
• Built a config_key -> ConfigOption lookup by reflecting over the static ConfigOptions fields, so known keys are enriched with their declared default value, default flag, and description.
• For unknown keys (not declared in ConfigOptions): default_value and description are NULL, and is_default is reported as true.
• Updated Spark engine documentation (procedures.md) with the new columns and usage examples.
• Updated GetClusterConfigsProcedureTest with assertions covering the new columns.

Tests

• GetClusterConfigsProcedureTest:
  • Verified the result schema has 6 columns with the expected field names.
  • Verified default_value, is_default, and description for an overridden key (e.g. kv.snapshot.interval).
  • Verified a key with no declared default reports NULL default and is_default = true.

API and Format

• Output schema (column set and order) of the sys.get_cluster_configs procedure is extended. This is an additive change; existing columns keep their positions. Downstream consumers reading by column index should be aware of the new trailing columns.

Documentation

• Updated website/docs/engine-spark/procedures.md to document the three new output columns and provide example output.