[OSPP] Provide A Common MQTT Mapper

[WillardHu]

What would you like to be added/modified:

• Provide a proposal;
• Craete a MQTT Mapper project and is working properly;
• The attribute value in MQTT message can be parsed by the CRDs of DeviceModel and Device, these serialization methods need to be completed: json, yaml and xml;

Why is this needed:

The MQTT protocol is the common device protocol in most device hardware markets. We want to have a common MQTT Mapper to handle these devices using the MQTT protocol, and it can support getting attribute values from the common serialization methods(i.e. json, yaml and xml). In order to fulfill the above requirements, we need you to complete these tasks:

1. We expect you to use the latest mapper-framework to add a Mapper for MQTT protocol to the project kubeedge/mappers-go;
2. We expect this Mapper can read the message from the topic of the specified MQTT service, And the attribute value can be parsed from the message by common serialization methods (i.e. json and xml);
3. (Optional)We expect you to provide a more scalable solution to parse attribute values from more custom messages;

Refer:

• https://github.com/kubeedge/kubeedge/blob/master/docs/proposals/device-crd-v1beta1.md
• https://github.com/kubeedge/kubeedge/tree/master/staging/src/github.com/kubeedge/mapper-framework