Updated lpe computation in examples

[ArCho48]

Modified all train.py files to activate graphgps transform. Updated lpe variable in json files.

[allaffa]

@jychoi-hpc
This is the branch we should use to re-generate the ADIOS-2 files.

[ArCho48]

@allaffa @kshitij-v-mehta made the necessary changes. Now,

1. graphgps_transform defined in the preonly block performs laplacian positional encodings, chemical encodings and topological encodings
2. laplacian positional encodings are within try/except loop and if missing, zero vectors are appended for each node

[kshitij-v-mehta]

I know Arindam may make some modifications to this PR, but I approve the current set of edits.

[ArCho48]

Thank you Kshitij. My updates should be ready by friday at the latest. I will invite you to review once again at that point.