Implement DS Get /ipam/prefix/available-prefixes

[theochita]

This DS Feature makes users able to get available prefix's in a parent prefix.

[fbreckle]

Why is this required if https://github.com/e-breuninger/terraform-provider-netbox/blob/master/netbox/resource_netbox_available_prefix.go exists?
I.e. if you want to get the next available prefix, then lifecycle it with terraform, why would you not just use the netbox_available_prefix resource?

[theochita]

Why is this required if https://github.com/e-breuninger/terraform-provider-netbox/blob/master/netbox/resource_netbox_available_prefix.go exists? I.e. if you want to get the next available prefix, then lifecycle it with terraform, why would you not just use the netbox_available_prefix resource?

Its for anyone who wants to know the available prefixes before hand for whatever reason.

In my own use case i need to know the available prefixes for multiple parent prefixes, then find one that fits my cidr and select only one that i want to create.

To my knowledge there's no way to do it in a not hacky way without this DS.