Scheduled reports: Download, a report for a period as a ZIP

inbuxa:ReportExport/set creates {reportId, from?, to?}: the report built
for that period (its last full one by default, at most 90 days back, as
far as metrics are kept) as a ZIP of summary.txt and the section CSVs,
stored as an upload, mailing nobody. Reading needs sysScheduledReportGet,
as seeing the report does; a tenant administrator downloads only their
own; every download is in the audit log. A download doesn't move the
deliverability baseline the next mail compares with.

crates/jmap/src/changes/get.rs

@@ -434,6 +434,7 @@ impl IntermediateChangesResponse {
             | MethodObject::SecurityAcceptance
             | MethodObject::DeliverabilityReport
             | MethodObject::DeliverabilitySettings
+            | MethodObject::ReportExport
             | MethodObject::ScheduledReport
             | MethodObject::ScheduledReportSettings
             | MethodObject::Journal