Fix deprecated serializer options, +TODO in prod!

config/packages/dev/jms_serializer.yaml

 jms_serializer:
     visitors:
-        json:
+        json_serialization:
             options:
                 - JSON_PRETTY_PRINT
                 - JSON_UNESCAPED_SLASHES

config/packages/jms_serializer.yaml

 jms_serializer:
     visitors:
-        xml:
+        xml_serialization:
             format_output: '%kernel.debug%'
 #    metadata:
 #        auto_detection: false

config/packages/prod/jms_serializer.yaml

 jms_serializer:
     visitors:
-        json:
+        json: # TODO: will crash in prod
             options:
                 - JSON_UNESCAPED_SLASHES
                 - JSON_PRESERVE_ZERO_FRACTION