[UX] Improve the output of `dstack ps`, `dstack fleet`, and `dstack apply`

[peterschmidt85]

1. For both dstack ps and dstack fleet, without --verbose, replace RESOURCES and SPOT with GPU (using the notation that the user specifies the GPU requirements, etc. A10:24GB:3 (spot))
2. For both dstack fleet, if placement is set to cluster, show BACKEND (with the region) only once on the right from the fleet name - to indicate that it's a cluster.
3. For dstack apply, without --verbose, replace RESOURCES and SPOT with GPU (see above), do not include INSTANCE, and replace the progress indicator "Launching ..." per job with the output of dstack ps.