feat(Interval/Set/Fin): new file (#22452)

Co-authored-by: Yaël Dillies <yael.dillies@gmail.com>

Author: urkud

Mathlib.lean

@@ -4514,6 +4514,7 @@ import Mathlib.Order.Interval.Multiset
 import Mathlib.Order.Interval.Set.Basic
 import Mathlib.Order.Interval.Set.Defs
 import Mathlib.Order.Interval.Set.Disjoint
+import Mathlib.Order.Interval.Set.Fin
 import Mathlib.Order.Interval.Set.Final
 import Mathlib.Order.Interval.Set.Image
 import Mathlib.Order.Interval.Set.Infinite