Enhance Network "get_next" methods to optionally allocate/reserve at the same time

[jathanism]

Yet another IPAM-related Network enhancement. Currently calling the next_network or next_address methods on a Network object will only show you eligible network objects, but will not actually create them.

Let's think about implementing an object flag or alternative endpoint that will allocate or reserve the networks in the same call.

Maybe it could be as simple as implementing support for POST to allocate/reserve, where GET only shows you what is available?

For example:

See the next two (2) available /28 networks:

GET /api/networks/1/next_network/?prefix_length=28&num=2

Automatically allocate the next two (2) available /28 networks:

POST /api/networks/1/next_network/?prefix_length=28

[rmhasan]

Hi @jathanism and @nickpegg PR #266 fixes this issue. Can someone review it.