* [cli] Write to stdout/stderr, allow redirection
Previously, slf4j-simple from generator core was being used. This writes
to only a single stream (STDERR) and is confusing from a CLI tooling
perspective.
This consumes logback in CLI, and excludes core's slf4j-simple
dependency. This allows us to define multiple appenders, one for STDOUT
and one for STDERR.
WARN messages and lower are written to STDOUT. ERROR is written to
STDERR.
* [cli] Limit logs to match prev implementation
* Remove slf4j-simple from core project, to avoid conflicts with consumer logger implementations
