Configure Datadog analytics rate
Created by: daxmc99
- Correct get env for Datadog tracing
- Make mux trace rate configurable
Part of https://github.com/sourcegraph/sourcegraph/issues/29651
Test plan
Tested locally with Datadog agent
Created by: daxmc99
Part of https://github.com/sourcegraph/sourcegraph/issues/29651
Tested locally with Datadog agent