Use display field in Record.__str__() to support future models

[markkuleinio]

This PR supersedes #388 for clarity, and should fix #417, example:

>>> ss = list(netbox.ipam.services.all())
>>> ss[0].ipaddresses
[1.1.1.1/32]
>>>

See also: netbox-community/netbox#5992 (= NetBox 2.11.0 added the display fields)

[markkuleinio]

In addition to this PR, do you @zachmoody see us adding new custom models in pynetbox as they appear in NetBox? I mean, I could add a PR adding models like extras.Tags and so on, if desired. But if we are not going to add new models frequently, I'm not sure about the benefit of adding them at all (unless there is a need like with the model fields).

[zachmoody]

In addition to this PR, do you @zachmoody see us adding new custom models in pynetbox as they appear in NetBox? I mean, I could add a PR adding models like extras.Tags and so on, if desired. But if we are not going to add new models frequently, I'm not sure about the benefit of adding them at all (unless there is a need like with the model fields).

Models were always intended to just handle outliers. Kind of a judgement call on when to move that behavior into the parent class. I'd say if more than a few models behave similarly we should think about it. This totally make sense though if display is going to be the new human-friendly field going forward.