network-config should allow dhcp client option values

[Ryan Harper]

DHCP clients can send specific values in the dhcp request such as hostname, lease time, client_id, vendor_id, etc.

The dhcp configuration option in v1, and v2 (and others) only has dhcp as a boolean.

v1:
network:
  version: 1
  config:
    - type: physical
      name: eth0
      mac_address: 00:11:22:33:44:55
      subnets:
        - type: dhcp
          hostname: myhostname
          client: client_id_1
          lease: 3600

Would render in eni:

auto iface eth0 dhcp
  hostname myhostname
  client: client_id_1
  lease 3600

[James Falcon (falcojr)]

Tracked in Github Issues as https://github.com/canonical/cloud-init/issues/3015