Fixes #8284, fixes #8548, maybe (when tested) #8285, #8298.

Replaces many (but not yet all) planner log messages with entries in a structured planning report. Those reports are comprised of "step reports", each of which corresponds to a subroutine of do_plan. The complete report may be formatted (in English) via a Display implementation. If planning from the blueprint_planner background task is successful, a report is attached to the BlueprintPlannerStatus::Targeted variant so that it may be displayed via omdb.

TODO:

• More and better tests
• Update for the rest of [29/n] [reconfigurator] separate out noop image source decision making #8596, in particular NoopConvertInfo
• Update for [??/n] blueprint planner logic for mupdate overrides #8456
• Update for Use timesync status to decide when to upgrade boundary NTP zones #8616
• Update for [reconfigurator] RoT planner support #8421