Add TODOs in SQL files for recurring billing expansion

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=144133707

java/google/registry/tools/sql/billing_data_view.sql

@@ -94,6 +94,9 @@ FROM (
         (SELECT tld FROM [%DEST_DATASET%.RegistryData] WHERE type = 'REAL')
     ), (
     -- Extract synthetic recurring events from view of Recurring data.
+    --
+    -- TODO(b/27562876): Drop this section of the query once we verify
+    -- that expanded OneTime events via MapReduce are correct and complete.
     SELECT
       id,
       kind,

java/google/registry/tools/sql/recurring_event_data_view.sql

@@ -19,6 +19,9 @@
 -- Since the only Recurring events are for automatic renewals, this means each
 -- row stands in for the renewal OneTime that would be created for a given
 -- Recurring event if it were materialized as individual explicit renewals.
+--
+-- TODO(b/27562876): Drop this query once we begin materializing Recurring
+-- billing events as synthetic OneTime events.
 SELECT
   id,
   kind,  -- Needed for joining Cancellation information downstream.