[Feature]: Add `region` property to SSH fleet configuration

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Problem

As SSH fleets/fleet instances may be located in different data centers (that is, in different local networks), it would be useful to distinguish them. The region(s) property, which is already supported for cloud providers, seems as a perfect candidate for this. For example, one NFS volume (that is not yet supported) may be available to some SSH instances, but not to the others, in this case, it would be useful to mark both the fleet and the NFS volume as belonging to the same "region" (e.g., datacenter).

Solution

1. Add an optional region property to the fleet configuration.
2. regions and region are mutually exclusive; for on-prem fleets, regions is not allowed, and region is optional, with none as the default value; for cloud fleets, region: foo is an alias for regions: [foo].

Workaround

No response

Would you like to help us implement this feature by sending a PR?

No