Add support for Custom Fields

[jrbeilke]

Netbox 2.10 introduced REST API support for managing custom fields:
netbox-community/netbox#5274

Should be able to add this to extras in python-netbox

[DarylStark]

This is already possible and I'm using it;

netbox.ipam.create_ip_address(
    address='192.168.26.10',
    custom_fields={
        'my_custom_field': 'my_value'
    }
)

[jagter]

This is already possible and I'm using it;

netbox.ipam.create_ip_address(
    address='192.168.26.10',
    custom_fields={
        'my_custom_field': 'my_value'
    }
)

It's already possible.