fix(perf-latency-ops): use dict with summary events
fix(perf-latency-ops): use dict with summary events

Base html template require events_summary dict with
severity name with events number

scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests