docs: missing documentation for enable_selector_executor, enable_sort_spill_stream_regroup, and enable_shuffle_sort settings

[sundy-li]

Missing Feature Documentation

Three session settings that control execution engine internals are implemented in Databend source but are not documented.

Settings

enable_selector_executor (default: 1)

• Enables the selector executor for filter expression evaluation.
• The selector executor uses SIMD-optimized selection vectors for faster predicate evaluation.

enable_sort_spill_stream_regroup (default: 1)

• Enables regrouping of sort spill streams by domain before merging.
• Reduces the number of merge passes needed when sort data is spilled to disk.

enable_shuffle_sort (default: 0)

• Enables shuffle sort for distributed ORDER BY operations.

Source Reference

• src/query/settings/src/settings_default.rs

What's Missing

• None of these settings appear in any documentation page

Suggested Location

• Settings reference page