MB-26470: Add documentation on the ownership of main DCP objects
MB-26470: Add documentation on the ownership of main DCP objects

In DCP we have connections objects, stream objects, backfill
objects and some task objects. Some of these objects own the other
object(s) and some of them just have a weak reference to other
objets. This commit has a map of such a relationship between the
main DCP objects.

Change-Id: I6428b37df62c2e24f13da1de7d20a7b4177f6ed2
Reviewed-on: http://review.couchbase.org/85487
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Dave Rigby <a09264da4832c7ff1d3bf1608a19f4b870f93750@couchbase.com>

daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine