properly log the lambda response correctly

boto returns a `StreamingBody`[1] response rather than a json struct.
We're currently just logging things like "Error calling lambda
o2-1-proxy with function error <botocore.response.StreamingBody object
at 0x7f74cd6e02e8>" which is obviously less than ideal. Also make the
tests properly reflect this - annoyingly it appears like we can't use
moto to reliably test this interface as the moto `mock_lambda` decorator
needs you to be running inside a docker container??

[1] https://botocore.amazonaws.com/v1/documentation/api/latest/reference/response.html#botocore.response.StreamingBody

app/clients/cbc_proxy.py

@@ -147,7 +147,7 @@ class CBCProxyClientBase(ABC):
 
         elif 'FunctionError' in result:
             current_app.logger.info(
-                f"Error calling lambda {lambda_name} with function error { result['Payload'] }"
+                f"Error calling lambda {lambda_name} with function error { result['Payload'].read() }"
             )
             success = False