Internal API used by CustomersDot only. It accepts an array of
upcoming reconciliations. Each upcoming reconciliation contains:
`namespace_id`, `next_reconciliation_date`, `display_alert_from`.

If one namespace_id exists in upcoming_reconciliations table, the
existing record is updated. Othewise it creates a new record.

If all records are processed sucessfully, it returns 200. Othewise,
it returns 400 error with the namespace_ids failed to process.

Changelog: added
EE: true