Add loopback 4096 ip address for multi-asic VS hwsku. (#5849)

What is the motivation for this PR?
The internal BGP sessions were not coming up in multi-asic VS because Loopback4096 interface was not added for ASICs in multi-asic minigraph if ansible/lab was used in inventory file.

sonic-mgmt/tests/kvmtest.sh uses ./testbed-cli.sh -t vtestbed.yaml -m veos_vtb deploy-mg vms-kvm-four-asic-t1-lag lab password.txt to generate the minigraph .
Rerefence:
https://github.com/Azure/sonic-buildimage/blob/87425a5b2b02ecd75f3de7e5174e37e053e31790/src/sonic-bgpcfgd/bgpcfgd/managers_bgp.py#L128

How did you do it?
Add loopback_4096 ip addresses for asic in ansible/lab inventory

How did you verify/test it?
Bring up multi-asic KVM testbed.
./testbed-cli.sh -t vtestbed.yaml -m veos_vtb -k ceos add-topo vms-kvm-four-asic-t1-lag password.txt
./testbed-cli.sh -t vtestbed.yaml -m veos_vtb -k ceos add-topo vms-kvm-four-asic-t1-lag password.txt
Ensure all BGP sessions are up

ansible/lab

@@ -140,6 +140,8 @@ sonic_multi_asic:
     num_asics: 6
     start_topo_service: True
     frontend_asics: [0,1,2,3]
+    loopback4096_ip: [8.0.0.0/32, 8.0.0.1/32, 8.0.0.2/32, 8.0.0.3/32, 8.0.0.4/32, 8.0.0.5/32]
+    loopback4096_ipv6: [2603:10e2:400::/128, 2603:10e2:400::1/128, 2603:10e2:400::2/128, 2603:10e2:400::3/128, 2603:10e2:400::4/128, 2603:10e2:400::5/128]
   hosts:
     vlab-07:
       ansible_host: 10.250.0.109
@@ -152,6 +154,8 @@ sonic_multi_asic_2:
     num_asics: 4
     start_topo_service: True
     frontend_asics: [0,1]
+    loopback4096_ip: [8.0.0.0/32, 8.0.0.1/32, 8.0.0.2/32, 8.0.0.3/32]
+    loopback4096_ipv6: [2603:10e2:400::/128, 2603:10e2:400::1/128, 2603:10e2:400::2/128, 2603:10e2:400::3/128]
   hosts:
     vlab-08:
       ansible_host: 10.250.0.112