metrics: Make it possible to disable logging on NullReporter

[bsimpson63]

The current NullReporter logs but doesn't send metrics

baseplate.py/baseplate/lib/metrics.py

Line 102 in 41ab42f

logger.debug("Would send metric %r", metric_line)

. This can be kind of noisy for local development so there should be an option to get it to not log.

[spladug]

Fixed in aec186f, thanks @bsimpson63 !