Revisit command-specific telemetry implementations

[tlmii]

In discussions with @jimmylewis about the changes necessary to make #430 work, there's agreement that the current need for an ITelemetry object to be passed into every command that needs specific info (in this case BaseHttpCommand-derived commands) is far from ideal.

But the current infrastructure of ICommand<> -> CommandWithStructuredBase<> -> BaseHttpCommand makes implementing a proper decorator pattern infeasible at this late stage.

Further, we're likely to be changing much of that infrastructure based on the System.CommandLine work, which may make this moot, easier or just different.

This issue is here to track the technical debt and make sure we address it later as that System.CommandLine work comes alive.