Display all statsd metrics in prometheus

[ysawa0]

Before, due to the "drop all" rule, statsd metrics that didn't match any rules were dropped in prom. I'm removing that so metrics not specified by a rule will be autogenerated. Should help in debugging the some of the metrics issues in #274 #275 #276
ex:

# HELP ratelimit_service_rate_limit_within_limit Metric autogenerated by statsd_exporter.
# TYPE ratelimit_service_rate_limit_within_limit counter
ratelimit_service_rate_limit_within_limit{domain="rl",key1="foo",key2="bar"} 12
# HELP ratelimit_service_response_time_seconds Metric autogenerated by statsd_exporter.
# TYPE ratelimit_service_response_time_seconds histogram
ratelimit_service_response_time_seconds_bucket{grpc_method="ShouldRateLimit",le="0.005"} 196
ratelimit_service_response_time_seconds_bucket{grpc_method="ShouldRateLimit",le="0.01"} 196

[mattklein123]

Thanks!