[UX] Improve dstack fleet output layout

[peterschmidt85]

dstack fleet didn't include fleet information, such as nodes, resources, spot, placement, etc.

Before:

   FLEET         INSTANCE  BACKEND  REGION       RESOURCES            PRICE   STATUS  CREATED
   gpu-cluster   0         aws      us-east-1    A100:80GB:8 spot     $28.50  busy    2 hours ago
                 1         gcp      us-central1  A100:80GB:8 spot     $26.80  busy    1 hour ago
   on-prem       0         ssh                   A100:40GB:4          -       busy    3 days ago
                 1         ssh                   A100:40GB:4          -       idle    3 days ago
   test-fleet    -         -        -            -                    -       -       10 min ago

After:

   NAME         NODES  GPU           SPOT       BACKEND       PRICE    STATUS  CREATED
   gpu-cluster  2..4   A100:80GB:8   auto       aws           $0..$32  active  2 hours ago
     instance=0        A100:80GB:8   spot       aws (us-ea…)  $28.50   busy    2 hours ago
     instance=1        A100:80GB:8   spot       gcp (us-ce…)  $26.80   busy    1 hour ago
   on-prem      4      -             -          ssh           -        active  3 days ago
     instance=0        A100:40GB:4   -          ssh           -        busy    3 days ago
     instance=1        A100:40GB:4   -          ssh           -        idle    3 days ago
   test-fleet   0..1   gpu:16GB      on-demand  *             -        active  10 min ago