[10/n] [sled-agent] make RackNetworkConfig ports a non-empty UplinkPorts newtype

[sunshowers]

In prior commits in the stack, we made it so that transient DB errors don't result in a partially-generated config. This change encodes one specific form of that (non-empty ports) into the type system.

Making bootstore deserialization fallible is an improvement in this case, because it turns a panic into a loop.

Also include a change to make the rack ID in StartSledAgentRequest a typed RackUuid. This isn't directly related but is spiritually similar and I'm touching this code anyway.

Depends on:

• [1/n] [sync-switch] build bootstore bgp peers from already-loaded port settings #10642
• [2/n] [sync-switch] move bootstore config building into nexus-switch-config #10643
• [3/n] [sync-switch] move bfd and address lot reads back to bg task, make the builder pure #10644
• [4/n] [sync-switch] replace db-model builder inputs with domain types #10645
• [5/n] [sync-switch] extract db translation into a new crate #10646
• [6/n] [sync-switch] factor switch_port_settings_get body out #10647
• [7/n] [sync-switch] add single-transaction switch config read (not yet wired up) #10648
• [8/n] [sync-switch] read switch config in one transaction #10649
• [9/n] [sync-switch] bail on an incomplete bootstore config instead of silently dropping items #10650