Add timestamp in ISO format including seconds and milliseconds

[sschulz92]

We have a few separate workspaces which are quite fast. If you compare the reports you cannot tell anyone which workspace was executed in which order since the timestamp propagated to the JSON-report is not containing seconds nor milliseconds.

At the moment the JSON-report contains the following format: "timestamp": "Jul 15, 2024 at 11:37am"

Would it be OK to add another field with - more or less - the same information but formatted like this: %Y-%m-%dT%H:%M:%S.%fZ

My versions:

$ gauge -v
Gauge version: 1.6.7
Commit Hash: 684d870

Plugins
-------
html-report (4.3.1)
json-report (0.4.0)
python (0.4.5)
screenshot (0.2.0)