RSDK-7903 Include unhealthy remotes in resource list with status

[maximpertsov]

Summary

Keep remote resources in the ResourceNames and MachineStatus APIs when their remote gets disconnected. In the latter API, mark such resources with a state indicate that they are disconnected.

Details

Robot clients now fetch and cache resource statuses via the GetMachineStatus API instead of resource names via ResourceNames API.

Open questions

• Should we add a new state for disconnected nodes? (e.g. NodeStateDisconnected), or is it sufficient to reuse the unhealthy state with a corresponding error (e.g. NodeStateUnhealthy[reason:disconnected])?
  • FWIW, I slightly prefer a new state given the proposed implementation, since a healthy but disconnected remote resource can appear as "disconnected" or "ready" depending on whether a client calls MachineStatus on the local or remote machine, respectively. Having a specialized state that can only appear for remote resources feels like the less confusing option in this case.
• Shall we bubble up remote update errors? (see this comment and this comment) - this will make the PR much noisier but might be the correct thing to do.

Depends on

• Expose unhealthy state + error: RSDK-8595 Unhealthy resource state #4257
  • Note that those changes are included in this PR as well - see this diff for changes excluding the dependent PR.
• RSDK-7843: Do not remove resources when a remote has a transient error. #4268 - specifically include the unit test from the PR since we want to satisfy the same invariant here.

[maximpertsov]

An alternative approach to the changes in this file is to define a new state (e.g. NodeStateDisconnected) - see the "Open questions" section in the PR description for more details and see the revert of this commit for a general idea of how this would look.

[maximpertsov]

the high-level change here is that a robot client now caches the results of MachineStatus rather than just ResourceNames. As a result, multiple tests that result on injecting a mock function for ResourceNames now need to mock MachineStatus.

[maximpertsov]

An alternative to defining a new state would be to mark disconnected resource nodes as "unhealthy" with an appropriate error message. See "Open questions" in the description of this PR for more details and revert this commit to see how this alternative approach would look.