Load checkpoints with eval_setup from different folder from training

[kerrj]

Previously, if one ran ns-train from a directory, then any call to eval_setup would have to be called from a directory where the relative layout of the outputs folder had to match training. I changed this to take into account the full path to the config.yml file in eval_setup so that it loads checkpoints folders not equivalent to the training folder.

For example, running this will fail:

ns-train ...
cd ..
ns-viewer --load-config nerfstudio/path/to/config.yml

There still needs to be some work to make data path agnostic to the running dir, but this so far at least makes it agnostic for the checkpoint folder.

One option is making data paths absolute, though this would break if you try to send checkpoints+data to other people, or move the original data dir around.