Include subnet name

[normelton]

This PR will pull an optional subnet name from the user-context of a subnet configuration and include it as a label:

"subnet4": [{
    "subnet": "192.168.0.0/24"
    "user-context": {
        "name": "My Test Subnet"
    },
    "pools": [ ... ]
}]

[Qwiko]

Nice find!
However I personally is not a huge fan of incorporating user-defined arbitrary fields in software that is meant to be used by a broad audience.

I think another approach of extending certain behavior outside of the actual code would be preferred so for users that have custom data they would like to be displayed could add that with some setting. Like a list of selected fields in the "user-context" they would like to extend. user-context.name for example would turn into some field like uc_name or the like in the actual metric.

[normelton]

I think another approach of extending certain behavior outside of the actual code would be preferred so for users that have custom data they would like to be displayed could add that with some setting

So that was my initial approach, but it seems the label names have to be configured when the metric is created. There doesn't appear to be a way to add an ad-hoc label once it's discovered from the Kea server's user-context block :(.

That said, if you have an idea, I'm happy to research/implement.