Elastic auto IP address function

[mikeingold]

I'm interested in adding support for Windows to ElasticManagers addr=:auto feature since it currently only supports Mac and Linux. I checked the source and found that the get_private_ip() function is just running shell commands for these specific platforms and throws an error otherwise. It looks like this functionality was added into Sockets as Sockets.getipaddr() as of Julia v1.2, which probably would've been a compatibility issue back when the get_private_ip() code was authored in 2020, but seems fairly reasonable now that even v1.6 is considered the LTS branch.

I don't mind making some changes and submitting a PR, but this would probably require bumping the Julia compat entry to 1.2, so I figured it would be worth asking the question first: how does the community feel about this? Is this a breaking change for anyone?