Fix newly added PANW threat schema, fix error logging, update avro dep (

#171)

- Fix newly added PANW threat schema breaking change (url_category_list:
string -> list<string>)
- Dont error!() log the whole mutated event on failure to cloudwatch
since we sideline the input event and this can be really huge.
- Improve some error string to include the failing log source table name
as this is impossible right now
- Note: most of the diff in transformer/main.rs is just whitespace while
adding a missing indent in process() lambda fn

data/managed/log_sources/panw/log_source.yml

@@ -951,7 +951,9 @@ schema:
                       - name: category
                         type: string
                 - name: url_category_list
-                  type: string
+                  type:
+                    element: string
+                    type: list
                 - name: url_idx
                   type: string
                 - name: user