feat: Add function to modify API requests

[amhn]

I looked into the behaviour of go-netbox a little more. Turns out it is possible to hook into the request before it is sent.

This let's us do two things:

• Drop required fields for the partial update request, making it possible to just send e.g. {"primary_ip4": 5} to the virtual-machines patch end point.
• Force fields to be sent even when go would have stripped them, because they are null, 0 or "". This allows us to set fields to their null value. E.g. primary_ip4, but also description, vcpus and all other not required fields.

I did only implement it for netbox_virtualization_vms yet. Let me know what you think of this approach. This would help for the primary_ip6 stuff, at the very least avoiding the forced renewal of IPs.

Fix #151 Fix #152

[smutel]

Hello,

I don't test your branch but it could be a good idea.

I am currently facing an issue with primary ip. When I change primary_ip4 field, I need to set the primary_ip6 with his older value. This does not work with concurrent calls on the same vm interface.

[smutel]

I will try to test it tomorrow

[amhn]

With this branch it is not needed to populate fields other than the ones that have changed.

There is still a concurrency issue in netbox which is triggered by changing primary_ip4 and primary_ip6 in parallell. I have seen that in the terraform_vault provider they work around this with mutexes per api endpoint. Perhaps this is worth looking at.

[smutel]

When I remove the CPU, the primary interface is removed also. With a tcpdump I saw the request args below:

{"primary_ip4":null,"primary_ip6":null,"vcpus":null}

[smutel]

I think it's due to https://github.com/smutel/go-netbox/pull/42. Perhaps it's better to revert it and to move forward with this PR ?

[smutel]

I tested it without https://github.com/smutel/go-netbox/pull/42 and it is working fine.
It will definitively help to add primary_ip field.