sink.ctf.fs: initialize structure fields

sink.ctf.fs: initialize structure fields

In preparation to using some C++ objects as fields.  Allocate with new
and deallocate with delete where relevant.

Change-Id: I924a6088b17e1d3ae4b8a239cf059fc3a7ecc8c6
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/12239
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>