fix(hubble): drain should not stop enricher (#5011)

currently hubble stops enricher when 'draining', but it shouldn't. 

background: drain should flush all indexed events on the 'indexing' side
(the part that'll run in spitzer). when migrating, we'll first start
draining, to ensure no events in hubble are in-flight, then we'll
migrate the hubble state into spitzer and start spitzer which will do
the logic that's deactivated in hubble in when draining