Change `track_usage_event` method to accept any value

This MR has beed merged recently !40475 (diffs)

With this we can include include Gitlab::Utils::UsageData in service and use method

track_usage_event(:"your event name", author)

Using this method I would say we do not need an extra class lib/gitlab/usage_data_counters/issue_activity_unique_counter.rb

Using this method will check a feature per event usage_data_<event_name>

Add track_usage_event from Gitlab::Utils::UsageData to docs