Apply data model from eos_cli_config_gen in eos_l3ls_evpn

```
tenants:
  # Tenant A Specific Information - VRFs / VLANs
  Tenant_A:
    mac_vrf_vni_base: 10000
    vrfs:
      TENANT_A_PROJECT01:
        vrf_vni: 11
        svis:
          311:
            name: 'PR01-TRUST-DHCP'
            tags: [POD01]
            enabled: true
            ip_address_virtual: 10.1.31.254/24
            ip_helpers:
              1.1.1.1:
                source_interface: lo100
```

Rendering is as below for eos_cli_config_gen:

```
  Vlan311:
    tenant: Tenant_A
    tags: ['POD01']
    description: PR01-TRUST-DHCP
    vrf: TENANT_A_PROJECT01
    ip_address_virtual: 10.1.31.254/24
    ip_helpers:
      1.1.1.1:
        source_interface: lo100
        vrf: TENANT_A_PROJECT01
```

And EOS configuration:

```
interface Vlan311
   description PR01-TRUST-DHCP
   vrf TENANT_A_PROJECT01
   ip address virtual 10.1.31.254/24
   ip helper-address 1.1.1.1 vrf TENANT_A_PROJECT01  source-interface lo100
```

Add knob to support source VRF to originate packets. If not set, current
VRF is used