[BUG] The datadog.process_agent.url attribute does not take datadog.site into account

[jeroenj]

E.g. if you're using the EU region for Datadog you'd set datadog.site to datadoghq.eu. At that point you expect anything within the agent to use that. However process traces are still shipped to datadoghq.com because datadog.process_agent.url defaults to https://process.datadoghq.eu. I'd have expected it to default to "https://process.#{node['datadog']['site']}".