Support internal IP and cluster placement for jarvislabs

[r4victor]

JarvisLabs backend now supports placement: cluster fleets, multi-node tasks, and connectivity between VMs via VPC internal IPs.

✗ dstack apply -f .dstack/confs/tasks/iperf.dstack.yml
 Project        main
 User           admin
 Type           task (nodes=2)
 Resources      cpu=2.. mem=8GB.. disk=100GB.. gpu=0..
 Spot policy    auto
 Max price      off
 Retry policy   off
 Idle duration  5m
 Max duration   off

 #  BACKEND                        RESOURCES                      INSTANCE TYPE  PRICE
 1  jarvislabs (india-chennai-01)  cpu=x86:2 mem=8GB disk=100GB   cpu-2x8        $0.0496
 2  jarvislabs (india-noida-01)    cpu=x86:2 mem=8GB disk=100GB   cpu-2x8        $0.0496
 3  jarvislabs (india-chennai-01)  cpu=x86:4 mem=16GB disk=100GB  cpu-4x16       $0.0992
    ...
 Shown 3 of 8 offers, $2.69max

Submit the run iperf3? [y/n]: y
 NAME      BACKEND                        GPU  PRICE    STATUS        SUBMITTED
 iperf3                                   -    -        running       11:33
    job=0  jarvislabs (india-chennai-01)  -    $0.0496  running       11:33
    job=1  jarvislabs (india-chennai-01)  -    $0.0496  provisioning  11:33

iperf3 provisioning completed (running)
-----------------------------------------------------------
Server listening on 5201 (test #1)
-----------------------------------------------------------
Accepted connection from 10.0.0.3, port 40718
[  6] local 10.0.0.2 port 5201 connected to 10.0.0.3 port 40726
[ ID] Interval           Transfer     Bitrate
[  6]   0.00-1.00   sec  4.55 GBytes  39.1 Gbits/sec
[  6]   1.00-2.00   sec  4.54 GBytes  39.0 Gbits/sec
[  6]   2.00-3.00   sec  4.62 GBytes  39.7 Gbits/sec
[  6]   3.00-4.00   sec  4.52 GBytes  38.8 Gbits/sec
[  6]   4.00-5.00   sec  4.57 GBytes  39.3 Gbits/sec
[  6]   5.00-5.00   sec  2.38 MBytes  32.7 Gbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate
[  6]   0.00-5.00   sec  22.8 GBytes  39.2 Gbits/sec                  receiver
Exited (0)