fix: fixed a bug from autoware pointcloud merger

[anhnv3991]

Description

• In autoware_pointcloud_merger, when a downsampling resolution is specified, the autoware_pointcloud_divider is used to downsample the input PCD files. The downsampled files are stored in a directory named pointcloud_merger_tmp/pointcloud_map.pcd. After that, the pointcloud merger iterates on the segmented files and merge them to a single output PCD file. However, the merger only uses a filesystem::directory_iterator to iterate on the pointcloud_merger_tmp directory, so it will not be able to detect any PCD files because they are put under the pointcloud_map.pcd directory. This PR replaces directory_iterator by recursive_directory_iterator, thus fixes that problem.

Related links

None

Tests performed

• Merged with downsampling resolution 0.2.

Notes for reviewers

None

Interface changes

None

Effects on system behavior

None

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