minor #20163 [Validator] Add errorPath to Unique constraint (thibaut22200)

This PR was squashed before being merged into the 7.2 branch.

Discussion
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[Validator] Add errorPath to Unique constraint

Document symfony/symfony#57436
and closes #19976

Commits
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23838fd [Validator] Add errorPath to Unique constraint

Author: javiereguiluz

reference/constraints/Unique.rst

@@ -170,6 +170,15 @@ collection::
 
 .. include:: /reference/constraints/_groups-option.rst.inc
 
+``errorPath``
+~~~~~~~~~~~~~
+
+**type**: ``string`` **default**: ``null``
+
+This option allows you to define a custom path for your message.
+``#[Assert\Unique(fields: ['latitude', 'longitude'], errorPath: 'point_of_interest')]``
+Instead of ``0: "Error message"``, it will be : ``0.point_of_interest: "Error message"``
+
 ``message``
 ~~~~~~~~~~~