[8.x] Add strict parameter to distinct validation rule (#6941)

* Add strict to disctinct validation rule

* Update validation.md

Co-authored-by: Taylor Otwell <[email protected]>

Author: gilbertorussi

validation.md

@@ -883,6 +883,10 @@ When validating arrays, the field under validation must not have any duplicate v
 
     'foo.*.id' => 'distinct'
 
+Distinct uses loose variable comparisons by default. To use strict comparisons, you may add the `strict` parameter to your validation rule definition:
+
+    'foo.*.id' => 'distinct:strict'
+
 You may add `ignore_case` to the validation rule's arguments to make the rule ignore capitalization differences:
 
     'foo.*.id' => 'distinct:ignore_case'