Add omdb sled-agent bootstore status

[andrewjstone]

I ended up creating an API type, BootstoreStatus, that is suitable for JSON / OpenAPI.

Fixes #4295 and #3722

[andrewjstone]

Output from running this on the testbed against the g0 sled-agent.

root@oxz_switch:~# omdb sled-agent --sled-agent-url http://[fd00:1122:3344:101::1]:12345 bootstore status
fsm ledger generation: 1
network config ledger generation: Some(1)
fsm state: initial_member
peers (found by ddmd):
    [fdb0:a840:2500:3::1]:12347
    [fdb0:a840:2500:5::1]:12347
    [fdb0:a840:2500:7::1]:12347
established connections:
     Pc { identifier: "g1", model: "i86pc" } : [fdb0:a840:2500:3::1]:12347
     Pc { identifier: "g2", model: "i86pc" } : [fdb0:a840:2500:5::1]:12347
     Pc { identifier: "g3", model: "i86pc" } : [fdb0:a840:2500:7::1]:12347
accepted connections:
    <none>
negotiating connections:
    <none>

[jgallagher]

LGTM 👍

I think your test failure is legit, but just an expectorate one