The implementation for the stub created in https://jira.mongodb.org/browse/SERVER-70932, i.e the read path. It will have two modes of operation

1. read and clear 

   {$telemetry: {clearEntries: true}}

1. read without clear (default)

   {$telemetry: {clearEntries: false}}

(1) will return a snapshot of the telemetry store at a point in time while (2) will not. Note, we should track and return a "first seen" timestamp for each entry as well as the time that entry was read/scanned. This is particularly important for (2) so that downstream consumers can determine if entries were evicted or not. Both modes should minimize blocking writes.