[CT-39] Bug: ensure that dump_graph is not run for logging events in cachy.py unless cache logging is turned on

[gshank]

We skip actual logging of core/dbt/adapters/cache.py in core/dbt/events/functions.py fire_event, but that doesn't prevent the actual 'dump_graph' call from executing, which is a performance problem.

In 0.21 we used a 'lazy_log' function to skip those events. We should re-implement something like that to prevent the overhead of these calls.