Use absolute paths for raw image 'label' attribute (camera.label)

[youngdjn]

We probably want to set up Metashape projects to store absolute paths to the raw images. This will make it easier to keep track of and locate raw image files programmatically, especially when images in the project come from multiple folders.

The important thing is to set the label attribute of each camera to the absolute path.

Note there is apparently a difference between the camera.photo.path (which appears to already be an absolute path, should confirm) and camera.label, which theoretically doesn't need to be a path at all it appears. But the camera.label value is what gets exported in the camera poses XML file, and it needs to contain the file path to enable MVMT downstream processing.

Probably just a simple change in this block.

Possibly relevant: It looks like the use of absolute paths can be set at the project level using project_absolute_paths See the docs, top of page 9. This however may affect camera.photo.path but not camera.label -- also need to confirm.

[youngdjn]

Completed via #23 (in the old repo).