Add configuration setting for mandatory surveys - refs BT#12915

This requires a DB change:

INSERT INTO extra_field (extra_field_type, field_type, variable, display_text, visible_to_self, changeable, created_at) VALUES (12, 13, 'is_mandatory', 'IsMandatory', 1, 1, NOW());

main/install/configuration.dist.php

@@ -473,6 +473,13 @@ $_configuration['agenda_colors'] = [
 // Requires DB change:
 // ALTER TABLE c_survey_invitation ADD answered_at DATETIME DEFAULT NULL;
 //$_configuration['survey_answered_at_field'] = false;
+// Add support to mandatory surveys. The user will not be able to enter to the course until fill the mandatory surveys
+// Requires DB change:
+/*
+INSERT INTO extra_field (extra_field_type, field_type, variable, display_text, visible_to_self, changeable, created_at)
+VALUES (12, 13, 'is_mandatory', 'IsMandatory', 1, 1, NOW());
+*/
+//$_configuration['allow_mandatory_survey'] = false;
 // ------
 //
 // Allow career diagram, requires a DB change: