Include accumulated warnings into output file(s)

It could be useful to add a section to the exported json metadata that holds info about problems that had been detected during processing.

In some use cases, the cmdline/console output is either being ignored or drowned in too much other output that important warnings about the trace data disappear into the aether.

Proposing something like this to be added to the output json:

{
  "otherData": {
     ...
     "issues": {
        "<warning_class1>": "reported_string/data",
        "<warning_class2>": "reported_string/data",
         ...
     }
  }
}

One approach (preferred) could be to make use of the TraceWarning class and adjust the exporter such that active trace warnings would be exported into the output json.