feat: Add metric for durations of symbolicate_event requests [NATIVE-185]

[loewenheim]

This is a continuation of #28565. It endows RealTimeMetricsStore (and its Redis implementation) with a function increment_project_duration_counter(project_id, timestamp, duration) that records the fact that at timestamp, we received a request for project project_id that took duration seconds to process. In the concrete Redis case, the event is first placed into a bucket based on the project id, bucket size, and time window; the bucket's value is a hash containing a counter for each 10-second interval of possible durations.

By way of example, assume these method calls (17 being a randomly chosen project id):

# at timestamp 1141, there was an event that took 28s to process
realtime_metrics.increment_project_duration_counter(17, 1141, 28)
# at timestamp 1145, there was an event that took 23s to process
realtime_metrics.increment_project_duration_counter(17, 1145, 23)
# at timestamp 1149, there was an event that took 54s to process
realtime_metrics.increment_project_duration_counter(17, 1149, 54)

Then the bucket symbolicate_event_low_priority:histogram:10:17:1140 contains the hash

{
    "20" : "2",
    "50" : "1"
}