enhancement for metrics

[HarrisChu]

Issue 1

generally there are three type metrics:

• latency
• succeed count
• error count

but not all of metrics with these three types.

e.g.

graphd

• num_sort_executors no latency
• num_aggregate_executors no latency
• optimizer_latency_us no count
• num_indexscan_executors no count
• num_opened_sessions no latency
• num_rpc_sent_to_metad no latency

storaged

• commit_log_latency_us no count
• num_send_snapshot no latency

Issue 2

more explicit metric name

graphd num_queries_hit_memory_watermark num_query_errors num_query_errors_leader_changes

num_query_errors = num_query_errors_leader_changes + num_queries_hit_memory_watermark num_queries_hit_memory_watermark should be num_query_errors_hit_memory_watermark?

do we have any other kind error?