Add useful metrics for ZK pipeline and request/server states

Add metrics to track time spent in the commit processor, watch counts and fire rates, how long a Zookeeper server is unavailable between elections, quorum packet size and time spent in the queue, aggregate request states/flow, request throttle, sync processor queue time, per-connection read and write request counts, commit processor queue sizes(read/write/commit), final request processor read/write times, watch manager cnxn/path counts, latencies at different points in pipeline for commits/informs, split up request type counters for more request types, export sum metrics for all AvgMinMax counters, per-connection watch fired counts, ack latency for each follower, percentile metrics to zeus latency counters, proposal count, number of outstanding changes,  snapshot and txns loading time during startup, number of non-voting followers, leader unavailable time, etc.