Move endpoint and tracing to top of HandlerFunc (#5460)
Move endpoint and tracing to top of HandlerFunc (#5460)

Move the logEvent.Endpoint and .Slug assignment as well as tracing to the
top of the HandlerFunc so a return cannot happen before the assignment.
Fixes cases where the endpoint is blank in logs in certain error cases.

Fixes: #5432
jsha/boulder,letsencrypt/boulder,jcjones/boulder,jcjones/boulder,letsencrypt/boulder,jcjones/boulder,jsha/boulder,jsha/boulder,jcjones/boulder,letsencrypt/boulder