Add multi-silo support

[sudomateo]

The cloud controller manager currently supports a single Oxide silo, requiring all Kubernetes cluster nodes to reside in the same silo with a single API endpoint and credential set. This limits cluster topologies and prevents deployments that span multiple silos or racks.

This work adds support for multiple Oxide silos, allowing a single Kubernetes cluster to manage nodes across different silos — including silos on different racks. This aligns the CCM with how Oxide customers operating multi-rack environments will need to deploy Kubernetes.

[sudomateo]

I used an LLM with MCP to chat about this first before creating the Linear issue and attaching a PLAN.md to the Linear issue. The PLAN.md isn't attached to the GitHub issue since GitHub doesn't have first party attachments and instead ties attachments to comments. Well, not really, technically an attachment can be posted in any GitHub comment but what I meant was there's no issue-level attachment like Linear.

For the curious I'm toying with the idea of some LLM flow where I can create issues and then use Linear attachments as sort of a state machine and/or artifact hub to have different agents or skills work through the issue via the attachments. For example, one skill can work with me to scope the issue and create the Linear issue and generate a PLAN.md. Then the next skill can work the issue by reading the PLAN.md and making the changes. Next, another skill can review the changes and post some REVIEW.md on the issue. Finally, another skill can use the REVIEW.md to spawn follow-up issues that the first agent will scope and create the PLAN.md. Rinse and repeat.