Database updates for respecting oversight within Echo

Provides the first step of adding and populating a new database field
for Echo oversight deployment.  The new field is populated via a
maintenance script and Event::loadFromRow will accept both new and old
results.  Everything will still run when the 2 now unused fields are
later dropped from the db.

Bug: 48059
Change-Id: I24d4b61a061f94ed9aaaa6087f33b2ab37f773cd
Merge "Database updates for respecting oversight within Echo"