capture more network information to improve waterfall

[vigneshshanmugam]

Couple of improvements that we can do to improve the step level waterfall in the UI

• Move the overall timing calculation logic in the UI to the agent to improve the performance feat: add request timing calculation for waterfall #168
• Use requestSentime and responseReceivedTime in favor of start/end time and use the monotonic clock in start
  and end time
• Capture the step index info for all the netinfo events to make querying easier
• Fix the timestamp to get the value of when the event got generated vs when the event is written to stdout which is after journey end.
  + [ ] Enhance the additional headers information by listening to requestWillBeSentExtraInfo and responseReceivedExtraInfo event
  + [ ] Figure out if an entry is from the cache by using requestServedFromCache event.

[paulb-elastic]

Removing capture web vitals and other RUM metrics - #120 from the list of requirements as we're tracking #120 separately.

[andrewvc]

Since we don't actually need the last two items for our UI right now I've crossed this out, and am closing the issue.