Create a view of the client portal

Creates a view of the client portal: which reports which client users see, in which order, with which brand and with which choice of periods. Both lists are required and neither may be empty. With send_notification the users are emailed, and that email is sent INSIDE the transaction that writes the view: a send that fails takes the write with it and answers 502 NOTIFICATION_FAILED, so nothing is left half done. The confirmation is CONDITIONAL: it is asked for only when the call would actually email somebody. Refusals: 400 VALIDATION_FAILED, UNKNOWN_PARAM, MISSING_REQUIRED_FIELD or INVALID_VALUE (a template among the reports, a staff user among the users, a repeat in either list), 403 WRITE_ACCESS_DISABLED, 404 NOT_FOUND for a report, a user or a brand template, 409 PORTAL_NOT_CONFIGURED when the portal has no subdomain or no email template plus the confirmation and idempotency conflicts, 429 EMAIL_QUOTA_REACHED, 502 NOTIFICATION_FAILED. if_version is not accepted.

Every write endpoint reads dry_run and idempotency_key; see the Write guarantees section of the introduction.