Add chartAttributes support

[bgreg1012]

While I was building my dashboards I found there's no support for drilldown links. It looks like support for chartAttributes is needed to get that feature, so I'd like to work on that and contribute a PR back.

[louism517]

@bgreg1012 - Please feel free. We'll be happy to receive your PR.

[bgreg1012]

@louism517 Quick question if you know, how is this repo related to go-wavefront-management-api? I was directed here from terraform-provider-wavefront, but I noticed in their code they use go-wavefront-management-api.