Add metrics for event travel time in the pipeline

We should be able to know the time it takes an event to travel in the pipeline from decode to sink stages.
The metrics should be per event type so we can know which events consume more time in the pipeline

No files or tests are named. Start by tracing the pipeline from the decode stage through the sink stage and locating existing metrics instrumentation. Define how elapsed travel time will be recorded per event type, then verify that the resulting metrics distinguish event types and cover the full pipeline.

Written by the indexing model from the issue text.