chore: Timezone fixes for ReportBuilder and for ReportController spec (#4246)

- ReportBuilder wasn't using the specified time zone for the timestamp in the
"build" method
- The ReportController spec was calling `Time.zone.today.to_time`, but
`Date#to_time` disregards the zone from `Time.zone` and reverts to the system
time zone.

app/builders/v2/report_builder.rb

@@ -19,7 +19,7 @@ class V2::ReportBuilder
   # For backward compatible with old report
   def build
     timeseries.each_with_object([]) do |p, arr|
-      arr << { value: p[1], timestamp: p[0].to_time.to_i }
+      arr << { value: p[1], timestamp: p[0].in_time_zone(@timezone).to_i }
     end
   end