Fix: mark "Spilling (to disk) Joins" as supported in features (apache#16343)

* Fix: mark "Spilling (to disk) Joins" as supported in features

* Fix: update support status for "Spilling (to disk) Joins" and add "Spilling (to disk) Sort Merge Join"

Author: kosiew

docs/source/user-guide/features.md

@@ -93,7 +93,8 @@
 - [x] Memory limits enforced
 - [x] Spilling (to disk) Sort
 - [x] Spilling (to disk) Grouping
-- [ ] Spilling (to disk) Joins
+- [x] Spilling (to disk) Sort Merge Join
+- [ ] Spilling (to disk) Hash Join
 
 ## Data Sources