Add stdin/stdout/stderr on invocation

[ghost]

runs:
[
  {
    "invocation": {
      "stdin": "...",
      "stdout": "...",
      "stderr": "...",
      ...
    }
  }
]

[michaelcfanning]

The current change draft resulted in some suggestions that will reset this change draft. At a high level, it was noted that this content could be copious (the question was posed whether we should limit the size of the string value). The primary suggestion was to make the property value a physical location. The URI for this could be a reference into content embedded in the files table, as usual. The physical location could also, presumably, refer to a region in a separate log file.

This suggestion minimizes complexity in the format but we lose the possibility of seeing the console output in clear text in the log file (which the TC seems comfortable with).