Add KeyFilter and deprecate KeyValue object

Signed-off-by: davidarendsen <davidarendsen@hey.com>

src/Expression/KeyValue.php

@@ -5,6 +5,9 @@ namespace Arendsen\FluxQueryBuilder\Expression;
 use Arendsen\FluxQueryBuilder\Type;
 use Exception;
 
+/**
+ * @deprecated
+ */
 class KeyValue extends Base
 {
     public const EQUAL_TO = '==';
@@ -204,4 +207,4 @@ class KeyValue extends Base
             throw new Exception('Operator "' . $operator . '" is not supported!');
         }
     }
-}
+}