Add a laser_scan_frame

[lowellausen]

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Previously the scan and point cloud had the same orientation when setting the point cloud frame as the value of the sensor frame. After the previous change (#195), they are off by 180 degrees regardless of which frame you set as the point cloud frame.

Lidar frame as the point cloud frame:

Sensor frame as the point cloud frame:

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Adding a separate laser_scan_frame parameter, so we can have by default the current behavior, where the scan data will be stamped with lidar frame. But it also gives us the possibility to stamp it with the sensor frame (as we do for the point cloud) and they keep being aligned.

I'm also opening a PR with this change, to be evaluated!

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Of course, also adding the transformation into the given frame would be ideal.

Targeted Platform (please complete the following information only if applicable, otherwise dot N/A):

• Ouster Sensor? N/A
• Ouster Firmware Version? N/A
• ROS version/distro? Humble
• Operating System? N/A
• Machine Architecture? N/A