Enable datadog and rollbar with environment variables

[joeystevens00]

This allows nexrender to support datadog and rollbar integrations by places values in the environment variables ENABLE_DATADOG_APM and ENABLE_ROLLBAR. Errors that come up in the worker will be reported to Rollbar and APM traces will be pushed to Datadog with a job UID in the span.

[inlife]

Hey @joeystevens00

Thanks for PR. Unfortunately can't merge it. This PR introduces quite a heavy dependency tree. And that goes against the primary principles of the library: https://github.com/inlife/nexrender#project-values

If something like that could be achieved with an optional-plugin-in-mind concept, that would be great!