Update collect_dast_scan_crawl_metrics_from_pipeline event definition to correct label field description

The collect_dast_scan_crawl_metrics_from_pipeline event yaml incorrectly defines label as the total scan time. Instead it is the total crawl time in milliseconds.

(Mike: I like that this captures total crawl time since we capture total scan time elsewhere)

Update the field description to correctly identify it as total crawl time in milliseconds. Most of our time fields are in seconds, so this could be unexpected.