src.ctf.fs: make ctf_fs_ds_group_medops_data_create return a unique_ptr

src.ctf.fs: make ctf_fs_ds_group_medops_data_create return a unique_ptr

Introduce ctf_fs_ds_group_medops_data_up, a unique_ptr type with a
deleter that calls ctf_fs_ds_group_medops_data_destroy.  Make
ctf_fs_ds_group_medops_data_create return (by parameter) a value of this
type.

Change ctf_fs_msg_iter_data::msg_iter_medops_data to be of this type too,
since the result of ctf_fs_ds_group_medops_data_create is put directly in
that field.

Change-Id: I971e2e6db622f5cfe492eaede239852886a24483
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/8272
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>