Add window duration property in aggregated profile proto (header)

[anvinjain]

There can be clock skew on backend machine resulting in start time and end time not being accurate values. Since we are depending on vertx timer for expiry of aggregation window(which uses stable clock), we know that expiry will happen correctly regardless of wall clock skew. So, additionally capturing duration of window in java objects. This needs to be added as a new field and serialized in aggregated profile proto as well.

Changes in aggregation window were made in this commit: a525979