Add support for PHP function strpos in expressions

Signed-off-by: Lompi <lompi91+github_com@gmail.com>

app/TransactionRules/Expressions/ActionExpressionLanguageProvider.php

@@ -60,6 +60,7 @@ class ActionExpressionLanguageProvider implements ExpressionFunctionProviderInte
 
             ExpressionFunction::fromPhp('substr'),
             ExpressionFunction::fromPhp('strlen'),
+            ExpressionFunction::fromPhp('strpos'),
         ];
     }
 }