Migrate all datetime columns to timestampz

rails/rails#41084 introduces support for timestamp with time zone

Currently, all our timestamp and datetime fields are without time zone (the previous default of datetime)

This has resulted in some inconsistencies when trying to query for a time object not explicitly passed as UTC

config/initializers/postgresql_timestamp.rb

@@ -0,0 +1,4 @@
+Rails.application.config.after_initialize do
+  # Use timestampz to create new timestamp columns, so that we get WITH TIME ZONE support
+  ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.datetime_type = :timestamptz
+end

db/migrate/20220831081937_migrate_timestamps_to_with_timezone.rb

@@ -0,0 +1,49 @@
+class MigrateTimestampsToWithTimezone < ActiveRecord::Migration[7.0]
+  def up
+    migrate_to_timestampz
+  end
+
+  def down
+    migrate_to_timestamp
+  end
+
+  private
+
+  def migrate_to_timestampz
+    execute <<~SQL.squish
+      DO $$
+      DECLARE
+      t record;
+      BEGIN
+        FOR t IN
+          SELECT column_name, table_name, data_type
+          FROM information_schema.columns
+          WHERE
+            table_schema = ANY (SELECT unnest(string_to_array(replace(setting, '"$user"', CURRENT_USER), ', ')) FROM pg_settings WHERE name = 'search_path')
+            AND data_type = 'timestamp without time zone'
+        LOOP
+          EXECUTE 'ALTER TABLE ' || t.table_name || ' ALTER COLUMN ' || t.column_name || ' TYPE timestamp with time zone USING ' || t.column_name || ' AT TIME ZONE ''UTC''';
+        END LOOP;
+      END$$;
+    SQL
+  end
+
+  def migrate_to_timestamp
+    execute <<~SQL.squish
+      DO $$
+      DECLARE
+      t record;
+      BEGIN
+        FOR t IN
+          SELECT column_name, table_name, data_type
+          FROM information_schema.columns
+          WHERE
+            table_schema = ANY (SELECT unnest(string_to_array(replace(setting, '"$user"', CURRENT_USER), ', ')) FROM pg_settings WHERE name = 'search_path')
+            AND data_type = 'timestamp with time zone'
+        LOOP
+          EXECUTE 'ALTER TABLE ' || t.table_name || ' ALTER COLUMN ' || t.column_name || ' TYPE timestamp without time zone USING ' || t.column_name || ' AT TIME ZONE ''UTC''';
+        END LOOP;
+      END$$;
+    SQL
+  end
+end