Reorder the sections of a report

Puts the sections of a report in another order and raises the version of its sections structure.

section_keys carries the same keys /v1/reports/get publishes for the report, each of them once, in the order they are to be read: a list that adds, drops or repeats a key is refused with 400 INVALID_VALUE instead of being merged onto what is stored, and a list that stopped being an exact permutation between the read and the write is refused with 409 VERSION_MISMATCH inside the transaction that writes -- that one carries the version the report is at and the reason, and no expected, because what went stale was the list of sections and not a number the caller sent. Read the report, rearrange the keys it gave you, and send them back.

It accepts if_version and compares it again inside that transaction. It changes nothing about what any widget shows or reads, so no cached result is dropped.

A report built on a template is refused with 400 APPEND_NOT_ALLOWED, reason template_based: its sections, and their order, belong to its template.

Refusals: 400 for the framework and the body, 400 INVALID_VALUE, 400 APPEND_NOT_ALLOWED, 403 WRITE_ACCESS_DISABLED, 404 NOT_FOUND, 409 VERSION_MISMATCH, 409 SECTION_BUSY and 409 REPORT_IN_TRASH.

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