Improved newsletter activity feed copy
Improved newsletter activity feed copy

refs https://github.com/TryGhost/Team/issues/1570
refs https://ghost.slack.com/archives/C02G9E68C/p1651581277636729?thread_ts=1651569897.474819&cid=C02G9E68C

Activity feed now shows 'Subscribed to newsletter – Weekly newsletter" text

TryGhost/Ghost,TryGhost/Ghost,TryGhost/Ghost