Update Device Defender demo to send custom metrics

[aggarw13]

This PR updates the device defender demo to demonstrate sending of custom metrics from a Linux platform to the AWS IoT Device Defender service. For more information on device-side custom metrics, refer to the AWS docs: https://docs.aws.amazon.com/iot/latest/developerguide/dd-detect-custom-metrics.html.

This PR makes the following changes:

1. Add support for collecting custom metrics for CPU usage time data (obtained from /proc/uptime) and System Memory data (obtained from /proc/meminfo)
2. Update utility for generating JSON report to support addition of custom metrics of string-list and number-list types for the 2 new metrics.
3. Update demo file to obtain the CPU usage time and memory data metrics from the support and add them to JSON report before sending to the Devide Defender service.
4. Update submodule for Device Defender library to access JSON report string literals relating to custom metrics.
5. Hygiene improvement of JSON report builder to use key names from Defender library instead of have them hard-coded in internal implementation so that either of short or long key names are used depending on user configuration of library.

Following is an example JSON report created from running the demo (Notice the custom metric objects of cpu-usage and memory-info at the end of the report):

{"header": {"report_id": 1613686957,"version": "1.0"},"metrics": {"listening_tcp_ports": {"ports": [{"port": 53},{"port": 53},{"port": 53},{"port": 22},{"port": 1883},{"port": 35853}],"total": 6},"listening_udp_ports": {"ports": [],"total": 0},"network_stats": {"bytes_in": 1139694747,"bytes_out": 2397302807,"packets_in": 67562100,"packets_out": 55610075},"tcp_connections": {"established_connections": {"connections": [{"local_port": 50094,"remote_addr": "127.0.0.1:35853"},{"local_port": 35853,"remote_addr": "127.0.0.1:50096"},{"local_port": 35853,"remote_addr": "127.0.0.1:50094"},{"local_port": 50096,"remote_addr": "127.0.0.1:35853"},{"local_port": 49044,"remote_addr": "<redacted>"},{"local_port": 22,"remote_addr": "<redacted>"},{"local_port": 41016,"remote_addr": "<redacted>"},{"local_port": 44402,"remote_addr": "<redacted>"}],"total": 8}}},"custom_metrics":{"cpu-usage": [{"number_list": [1348437120,1208020352]}],"memory-info": [{"string_list": ["8150792kB","7011132kB"]}]}}

[aggarg]

Can the following 4 macros be combined and thereby written in one snprintf call as opposed to 5 snprintf calls?

[aggarw13]

Sure, done. I was trying to separate out the formats of number-list and string-list through macros to make the different formats easier for the reader to see.

[aggarg]

Combining the 5 macros into one could reduce all this code into:

#define JSON_REPORT_FORMAT_PART5    \
    "\"custom_metrics\":{"          \
    "\"cpu-usage\":["               \
    "{"                             \
    "\"number_list\":["             \
    "%lu,"                          \
    "%lu"                           \
    "]"                             \
    "}"                             \
    "],"                            \
    "\"memory-info\":["             \
    "{"                             \
    "\"number_list\":["             \
    "%u,"                           \
    "%u"                            \
    "]}"                            \
    "]"                             \
    "}"                             \

    /* Write custom metrics. */
    if( status == ReportBuilderSuccess )
    {
        charactersWritten = snprintf( pCurrentWritePos,
                                      remainingBufferLength,
                                      JSON_REPORT_FORMAT_PART5,
                                      pMetrics->pCustomMetrics->cpuUsageStats.upTime,
                                      pMetrics->pCustomMetrics->cpuUsageStats.idleTime,
                                      pMetrics->pCustomMetrics->memoryStats.totalMemory,
                                      pMetrics->pCustomMetrics->memoryStats.availableMemory );

         if( !SNPRINTF_SUCCESS( charactersWritten, remainingBufferLength ) )
        {
            LogError( ( "Failed to write part 5." ) );
            status = ReportBuilderBufferTooSmall;
        }
        else
        {
            remainingBufferLength -= charactersWritten;
            pCurrentWritePos += charactersWritten;
        }
    }

[aggarw13]

Done

[aggarg]

The only other function that has lineNumber is GetEstablishedConnections which uses it to skip the first line.