[WIP] facts.inventory: add DNS search domain to all DHCP pools

[kylerisse]

Description of PR

Adds DNS search domain to all DHCP pools.

Tests

1. > nix build .#scaleInventory
2. Reviewed output of DHCP checking v4 pool

{
        "subnet": "10.128.10.0/24",
        "id": 10128100,
        "user-context": {
          "vlan": "cfInstl"
        },
        "pools": [
          {
            "pool": "10.128.10.80 - 10.128.10.254"
          }
        ],
        "option-data": [
          {
            "name": "routers",
            "data": "10.128.10.1"
          },
          {
            "name": "domain-search",
            "data": "scale.lan"
          }
        ]
      }

3. Reviewed output of DHCP checking v6 pool

{
        "subnet": "2001:470:f026:507::/64",
        "id": 25863,
        "user-context": {
          "vlan": "cfSigns"
        },
        "pools": [
          {
            "pool": "2001:470:f026:507:d8c::1 - 2001:470:f026:507:d8c::800"
          }
        ],
        "option-data": [
          {
            "name": "domain-search",
            "data": "scale.lan"
          }
        ]
      },

4. > nix build .#checks.x86_64-linux.core