Need for allowing customization of MQTT broker

[prasadjaywant]

Describe the issue
There is need to change attributes and telemetry in the broker configuration based of customer needs. However a MQTT broker is hardcoded currently for sending a few standard data samples. It needs attention to customize the broker to allow data keys and values as per customer needs. A set of easy instructions like in other documentation is proposed.

Configuration (Attach your configuration file)
Notate: Remove Access token from file if you want to attach a tb_gateway.json
Configuration file attached.

mqtt configuration.txt

Connector name (If you need help with some connector/converter):
[e.g. MQTT Connector] "MQTT"

Error traceback (If it was raised):
Missing data as in additional information below.

Versions (please complete the following information):

• OS: As in ThingsBoard Cloud
• Thingsboard IoT Gateway version: Latest as in ThingsBoard Cloud
• Python version: As in ThingsBoard Cloud

Additional context

1. We set up broker as per 'docker run -it -p 1884:1884 thingsboard/tb-gw-mqtt-broker:latest'.
2. Also filled up data points (8 attributes and 2 telemetry keys) as per instructions mentioned for 'Connection to broker' and 'Data mapping' in the MQTT configuration.
3. It was observed that the broker does not forward all configured datapoints. The converter log shows that only 3 data points (2 attributes and 1 telemetry only for every send) are entering the gateway connector. For instance jSON is as below; [json_mqtt_uplink_converter.py] - json_mqtt_uplink_converter _convert_single_item - 133 - Converted data: ConvertedData(deviceName=Demo Device, deviceType=default, telemetry=[TelemetryEntry(ts=1781976641883, metadata={}, values={DatapointKey(key=humidity, report_strategy=None): 65.0})], attributes=Attributes(values={DatapointKey(key=frequency, report_strategy=None): 84.0, DatapointKey(key=power, report_strategy=None): 90.0}), metadata={'receivedTs': 1781976641883}).
4. Issue: 6 out of 8 attributes and 1 of 2 telemetry keys are always missing in every payload.
5. Inference: Broker needs customization beyond hardcoded data samples (3 inbuilt).