Configuring Envoy to initiate tracing

There are a couple of ways of initiating traces when using envoy. I was wondering if there's a way to configure the `random sampling` or the `start child span` options. Is this something the [envoy bootstrap template](https://www.consul.io/docs/connect/proxies/envoy.html#envoy_bootstrap_json_tpl) would solve?

> By an external client via the x-client-trace-id header.
> By an internal service via the x-envoy-force-trace header.
> Randomly sampled via the random_sampling runtime setting.
> The router filter is also capable of creating a child span for egress calls via the start_child_span option.

https://www.envoyproxy.io/docs/envoy/v1.10.0/intro/arch_overview/tracing#arch-overview-tracing

Start with the Envoy bootstrap template linked in the issue and the Envoy tracing documentation for random_sampling and start_child_span. Determine whether Consul exposes these settings and what configuration change would be required; done means a supported configuration path or a clear explanation that it is not currently available.

Written by the indexing model from the issue text.