Add more sophisticated internet connectivity checker

[ConnorRigby]

This adds the ability to detect sneaky firewalls or anything else that may give false positives on internet connectivity by checking that a valid SSL connection can be made to a list of hosts.

[fhunleth]

@ConnorRigby I made some changes in the ssl-connectivity-checker-fh branch to pull more of the ping-related code to the behavior. I think there shouldn't be any case statements in the core now. Could you see if you like this.

Other things that I'm thinking about:

1. The VintageNet.Connectivity.SSLPing.ConnectOptions behaviour only had one function. It seems like making a behaviour isn't needed and we just pass a function around for this. However, since so many cases don't require runtime options, how about passing the ssl options with :host and :port too?
2. The example was with AWS IoT, but AWS IoT has a one-connection policy. That means that if the device is already connected, the SSL ping can cause AWS to break the current connection after it authenticates. (I actually don't know when AWS IoT breaks old connections, but it seems that after a mutual auth completes, it could do this.) I think we should pick a different example server.

Overall, I think this is looking really good.

[ConnorRigby]

The VintageNet.Connectivity.SSLPing.ConnectOptions behaviour only had one function. It seems like making a behaviour isn't needed and we just pass a function around for this. However, since so many cases don't require runtime options, how about passing the ssl options with :host and :port too?

I think passing a function around is fine. I just added the behaviour for easy typing. I think a typespec will also suffice. Should i change it back to the {module, function, args} version instead of just a module?

The example was with AWS IoT, but AWS IoT has a one-connection policy. That means that if the device is already connected, the SSL ping can cause AWS to break the current connection after it authenticates. (I actually don't know when AWS IoT breaks old connections, but it seems that after a mutual auth completes, it could do this.) I think we should pick a different example server.

how about github.com?

[ConnorRigby]

The changes in your branch look great to me.