This PR moves the definition of the `log_filter` default value from the `structopt` annotation
to the `trogging::Builder`. This allows users of `trogging` to define their own default value
for the log level.
This PR factors out the tracing/logging CLI optinos into the `trogging` utility crate,
so that multiple binaries from the IOx suite (such as conductor) can use the same (and quite complex)
logging/tracing configuration options (flags and env vars).
Closesinfluxdata/conductor#343