Probe: more detailed information about RPCs

probe.sh rpcs currently only returns the number of multicasts, anycasts and unicasts (async and sync) since the last reset. Add 3 additional keys:

• rpcs-enable-details: captures detailed information from now on. This is not enabled by default as capturing this information is costly (hashmap put/get, timing of RPCs etc)
• rpcs-disable-details: disables capturing of details
• rpcs-details: dumps detailed information (needs to be enabled before)
  • For async RPCs: number of RPCs for every destination (unicast or multicast)
  • For sync RPCs: ditto, plus min/max/avg invocation times