Add opt-in extended activity tracking with activity_metrics entity#1467

Matus Tomlein (matus-tomlein) merged 4 commits intorelease/4.8.0snowplow/snowplow-javascript-tracker:release/4.8.0from

feature/extended-activity-trackingsnowplow/snowplow-javascript-tracker:feature/extended-activity-trackingCopy head branch name to clipboard