Restoring dendrite state on scrimlet cold boot.

[rcgoodfellow]

When a scrimlet restarts, the switch zone restarts, or Dendrite restarts, Dendrite state needs to be repopulated.

When Dendrite comes up, it sends a Nexus a message saying it's up. This means that whatever state Nexus thought Dendrite had is now gone. So at this point, Nexus needs to calculate all the state that needs to be on that switch and use the Dendrite API to repopulate the state.

[rcgoodfellow]

From the call:

We want to add a new specific omicron internal endpoint for this. Similar to sled_agent_put but for dendrite.

• https://github.com/oxidecomputer/omicron/blob/main/nexus/src/internal_api/http_entrypoints.rs#L90

[morlandi7]

Closing this one as remaining related work is outlined in #4715