Make `resource_type` a different type in RunGetDetailed

[William Eliot]

When a run fails, it might fail before a resource has even been allocated due to validation or some other error. Therefore resource_type is None, which isn't a str.

So the resource_type field in RunGetDetailed should probably update to account for this fact. But the actual type of resource_type should probably be thought about more. For instance I think you could potentially train on multiple GPUs which aren't all the same type.

[stale]

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