studio: Add a UserAgent to the data submitted to the ingress.

[abernix]

Add a UserAgent to the data submitted to the ingress.apollo-spaceport/src/server.rs:

Name to be finalised, but candidate: ApolloRouterPluginUsageReporting

[garypen]

@glasser Noted that the name ApolloRouterPluginUsageReporting wasn't really descriptive since the spaceport isn't a plugin: "eh, it's not really a plugin? i think it would be fine to say apollo-spaceport or something."

There is a "standard": https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/User-Agent

and that seems fairly solid, I think having a version in there will pay off in the long term, so:

product: std::env!("CARGO_PKG_NAME"),
version: std::env!("CARGO_PKG_VERSION")
comment: usage reporting

which yields:

user-agent: apollo-spaceport / 0.1.0-preview.1 usage reporting

(which is consistent-ish with the header we put in the actual studio report:

        header.agent_version = format!(
            "{}@{}",
            std::env!("CARGO_PKG_NAME"),
            std::env!("CARGO_PKG_VERSION")
        );