Allow fine-grain logging to be configurable via CLI arguments

Title: Allow fine-grain logging to be configurable via CLI arguments

Description:

As discussed in Slack, it's currently not possible to change the fine-grain logging using CLI arguments. Currently it can only be configured via an admin endpoint. This is inconvenient because when deploying on Kubernetes, I can't easily configure the fine-grain logging building a container of my own. It's difficult (or at the very best a hack like a postStart with a sleep) to do it with a plain envoy image.

Suggestion: The suggestion given in Slack that @paul-r-gall and @botengyao seemed to prefer was the following:

Rather than having --enable-fine-grain-logging it would take configuration similar to --component-log-level, so something like --fine-grain-log-level(s) <string>.