ECX L2 conn: add possibility to select device interface

[mikouaj]

Use-case

Create layer2 connection with device on a-zide with possibility to select particular interface on a device.

Attempted Solutions

When using Web portal, it is possible to select device interface (by name) when creating layer2 connection.

Under the hood, POST on /ecx/v3/l2/connections is triggered with interfaceId attribute, ex:

  ...
  "virtualDeviceUUID": "ebb5b6d6-17ae-4ecc-a837-eac291c7adeb",
  "interfaceId": 7

InterfaceId corresponds to device interface identifier.
It is possible to retrieve interface identifiers along with names using from GET /ne/v1/device/<uuid>, ex:

interfaces": [
    {
      "id": 1,
      "name": "GigabitEthernet1",
      "macAddress": null,
      "status": null,
      "type": "MGMT",
      "ipAddress": null,
      "assignedType": "Equinix Managed"
    },
...

Proposal

Add interface_id argument to equinix_ecx_l2_connection resource schema.