[reconfigurator] Only provision to zpools with in-service physical disks

[smklein]

• Expand reconfigurator's Policy, SystemDescription to be aware of "what disks back zpools".
• Updates callsites iterating over "all zpools" to consider whether or not they only want provisionable zpools, using active + in-service disks.
• Adds a method sled_ensure_zones_not_using_expunged_disks, which can be used to remove zones using expunged disks.
  • This implementation leaves some TODOs, however, as it depends on [WIP] [reconfigurator] start removing expunged zones #5211 , and partially depends on [nexus] Make nexus aware of zone filesystems #5050

Partial fix of #5372

[smklein]

This seems to match the pattern below of "if we have any changes to make, do them and stop making further changes".

It seems plausible that we could remove an expunged zone and also do other allocations, but I'm not sure what our motivation is for "updating the blueprints via small steps", and wasn't confident enough to break that mold.

[smklein]

This method is currently acting as a no-op, because of the TODOs below.

But I think the right action here would be to add the zones to an "expunged zone" field within the blueprint?

@sunshowers , do you think #5211 will support that? Or will I need to add a BTreeSet to the BlueprintBuilder for each zone type that could be removed?

[smklein]

This PR is in merge hell and has been replaced by:

• [common] Share a common implementation of ZpoolName #5600
• [reconfigurator] Only place Crucible zones on provisionable zpools #5601
• [nexus] Remove zones on expunged disks #5599