Replace all previously text-based json fields with JSONBlob

This JSONBlob field type is a wrapper around Django's new generic
JSONField, but with the database column type forced to be text.  This
should behave close enough to our old wrapper around
django-jsonfield's JSONField and will avoid needing to do the
out-of-band database migration.

awx/main/migrations/_squashed_30.py

@@ -29,7 +29,7 @@ SQUASHED_30 = {
         migrations.AddField(
             model_name='job',
             name='survey_passwords',
-            field=models.JSONField(default=dict, editable=False, null=True, blank=True),
+            field=awx.main.fields.JSONBlob(default=dict, editable=False, blank=True),
         ),
     ],
     '0031_v302_migrate_survey_passwords': [