Add worker thread and LUA filter for common info

Based on the recommendations and feedback from FluentCon 2021, make the following updates:

Add a dedicated worker for the `stdout` plugin to ensure we maximise throughput. In fact indicate this is a recommendation for all output plugins (it helps to quickly drop the out-of-order retries in Loki for example). For Loki, probably want to set `retry_limit 0` as well to immediately drop: https://docs.fluentbit.io/manual/administration/scheduling-and-retries#configuring-retries 

Use a LUA filter to pick up any and all environment variables matching annotations/labels applied by CAO. Current approach uses a modify-nest filter pipeline but modify only works for valid variables (if not present it exits as a failure) and we just want to add any/all available (if not available then not an issue) plus ensure future-proofing. All the feedback from yesterday shows LUA is both powerful and performant although we likely want to monitor as well.