System attributes in device allocation resource

[chrismarget-j]

This PR introduces support for controlling system attributes of switch systems only via a new configuration block in the apstra_datacenter_device_allocation resource:

resource "apstra_datacenter_device_allocation" "test" {
  blueprint_id = local.blueprint_id
  node_name                = "Spine1"
  initial_interface_map_id = "Juniper_vQFX__AOS-7x10-Spine"
//  deploy_mode            = "drain"      <------ this attribute is deprecated
//                                             (moved to the system_attributes block)

  // the system_attributes block is new
  system_attributes = {
    name          = "Desired GUI Label"
    hostname      = "desired.host.name"
    asn           = 1234
    deploy_mode   = "drain"
    loopback_ipv4 = "192.0.2.2/32"
    loopback_ipv6 = "2001:db8::22/128"
    tags          = ["2", "22", "222"]
  }
}

Closes #502
Closes #503
Closes #504

[bwJuniper]

Amazing :)