The rollup indexer uses a range query to select the next page
of results based on the last time bucket of the previous round
and the `delay` configured on the rollup job. This query uses
the `epoch_millis` format implicitly but doesn't set the `format`.
This result in errors during the rollup job if the field
definition doesn't allow this format. It can also miss documents
if the format is not accepted but another format in the field
definition is able to parse the query (e.g.: `epoch_second`).
This change ensures that we use `epoch_millis` as the only format
to parse the rollup range query.