test(release): rehearse the Scheduling upgrade and the Casework BReg-source repin

[jeremi]

docs/site/src/content/docs/operate/advanced/upgrade-and-retire.mdx ("Upgrade in this order") lists steps for BReg, Casework, Evidence, and the clients only. It has no Scheduling step, although from v0.36.0 Scheduling needs identity.databaseId and one schedulingctl apply --runtime-config FILE before the upgraded runtime starts, and an upgraded runtime refuses to start without them. release/scripts/rehearse-upgrade.py does not exercise Scheduling either, nor the Casework BReg-source repin.

The v0.36.0 release notes work around the gap by pointing at their own Scheduling section. The runbook should carry it:

• a Scheduling step, with its database, package, and runtime-file backups and the schedulingctl plan / apply / status activation;
• where it sits relative to the clients;
• the same coverage in rehearse-upgrade.py.

[jeremi]

Update: the v0.36.0 release PR (#1739) added a Scheduling backup and activation step to "Upgrade in this order" and gave every BReg and Casework command there its required flags. What remains:

• "Roll back" in upgrade-and-retire.mdx has no Scheduling entry;
• release/scripts/rehearse-upgrade.py exercises neither Scheduling nor the Casework BReg-source repin.

[jeremi]

Update: #1739 now also covers Scheduling (and returning BReg and Casework to the previous release) in "Roll back". What remains here is release/scripts/rehearse-upgrade.py, which exercises neither Scheduling nor the Casework BReg-source repin.