fix: findDistinct with polymorphic relationships (#13875)

Fixes `findDistinct` with polymorphic relationships and also fixes a bug
from https://github.com/payloadcms/payload/pull/13840 when
`findDistinct` didn't work properly for `hasMany` relationships in
mongodb if `sort` is the same as `field`

---------

Co-authored-by: Patrik Kozak <35232443+PatrikKozak@users.noreply.github.com>

test/database/getConfig.ts

@@ -132,6 +132,17 @@ export const getConfig: () => Partial<Config> = () => ({
           hasMany: true,
           name: 'categories',
         },
+        {
+          type: 'relationship',
+          relationTo: ['categories'],
+          name: 'categoryPoly',
+        },
+        {
+          type: 'relationship',
+          relationTo: ['categories'],
+          hasMany: true,
+          name: 'categoryPolyMany',
+        },
         {
           type: 'relationship',
           relationTo: 'categories-custom-id',