remove types.Event and replace with database.Event

Created by: coury-clark

This PR refactors all usages of types.Event to instead use database.Event. Reason being is it was very strange that the EventLogStore insert operations take in a database.Event but the read operations return a types.Event. I need to make some updates here, and since there is already significant overlap I just refactored them all to use database.Event.

Test plan

I started Sourcegraph and ensured events can insert, read, and pings can be created correctly. Also looking for CI passing for some additional confidence here.