Adding awx_ as well as tower_ variable names for webhooks (#11925)

Adding utility to ease testing webhooks from command line
Modifying all variables to use a constants list of variable names

awx/main/constants.py

@@ -95,3 +95,8 @@ CONTAINER_VOLUMES_MOUNT_TYPES = ['z', 'O', 'ro', 'rw']
 MAX_ISOLATED_PATH_COLON_DELIMITER = 2
 
 SURVEY_TYPE_MAPPING = {'text': str, 'textarea': str, 'password': str, 'multiplechoice': str, 'multiselect': str, 'integer': int, 'float': (float, int)}
+
+JOB_VARIABLE_PREFIXES = [
+    'awx',
+    'tower',
+]