arduino: use forwardable subdomain as service endpoint

[Alan Noble]

Currently, the client’s service endpoint is hardcoded to vidgrind.ausocean.org. It is proposed to use the endpoint data.ausocean.org, which can be redirected as needed by means of DNS forwarding.

[Alan Noble]

Upon further investigation, DNS forwarding only supports forwarding of domains, not domains plus paths. A simple redirector app is therefore required to implement this feature.

[Alan Noble]

This is implemented by https://github.com/ausocean/cloud/tree/master/cmd/datablue, which implements a simple forwarding service from http://data.cloudblue.org to http://vidgrind.ausocean.org.