MDL-56567 competency: Course module competency option to override grade

Previously, if a course module had already been graded, course module
completion linked to the course module would not update. This
commit adds the option to enable overriding the grade at the course
module competency level.

This ensures that if enabled and a user completes a module associated
with a competency, that competency will be graded appropriately.

competency/classes/course_module_competency.php

@@ -71,6 +71,10 @@ class course_module_competency extends persistent {
                 'default' => self::OUTCOME_EVIDENCE,
                 'type' => PARAM_INT,
             ),
+            'overridegrade' => array(
+                'default' => false,
+                'type' => PARAM_BOOL
+            ),
         );
     }