Silent failure if binding output from Function cannot be decoded as JSON (Python binding)

[stewartadam]

When any part of the output message cannot be successfully parsed as JSON, the output binding will silently place the entire output as the value of the kafka message as a fallback.

I think it would be nice if a debug message was added here so that troubleshooting could be made easier, by viewing the function logs.

See also:

• MicrosoftDocs/azure-docs#104178
• #420