fix(coderd/database): aggregate user engagement statistics by interval (#16150)

This PR addresses the TODO comment here:

https://github.com/coder/coder/pull/16134/files#diff-1844f895bb005f036da11d800fe2a76b54bfddd481c5d8cb15f210c64679caa5R47

The backend now backfills entries for dates with no status changes.

coderd/database/dbauthz/dbauthz_test.go

@@ -1712,6 +1712,7 @@ func (s *MethodTestSuite) TestUser() {
 		check.Args(database.GetUserStatusCountsParams{
 			StartTime: time.Now().Add(-time.Hour * 24 * 30),
 			EndTime:   time.Now(),
+			Interval:  int32((time.Hour * 24).Seconds()),
 		}).Asserts(rbac.ResourceUser, policy.ActionRead)
 	}))
 }