Define new atoms to better log and understand various user journeys,
such as user switches, user starts, and user creation.
The UserLifecycleJourneyReported atom defines a user's journey and
holds a user's information such as their user id, user type, and flags
associated with the user. This atom includes a session-id which is used
to link to the UserLifecycleEventOccurred atom which keeps track of
lifycycle events that occur throughout a user's journey. As more user
journeys are defined, there could be more Events added in the future.
Note: the JourneyReported atom can currently be logged more than once
per user journey since there is no record of the user's ongoing journey.
This will be updated in a future CL.
Bug: 146505521
Bug: 150788910
Test: statsd_testdrive 264 265
Change-Id: Iff3847be64d718fb2ec17e58c33d47f7fa4b627a
acb5634dc4