Emit logstash records in ECS 1.7.0 format (v2)

This is a followup to c9a8fa22.

Among other changes, user.* now contains info about the user who
initiated an operation (e.g. through spiderpig) and user.effective.*
will have info about the account running the process (if they're
different).

I used https://doc.wikimedia.org/ecs/validator.html?forcecachemiss=true
to validate that a log record generated with this new code passes the
validator without errors.

Bug: T279086
Bug: T397967

Edited by Ahmon Dancy

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