Lagrangian post-processing should be renamed.

[OGaboriault]

In the parameter file, it is the only parameter starting with a capital letter. Also, the output file it is generating should be renamed since we have two post-processing tool now. (Force chains and this)

[acdaigneault]

Renaming the output files for the post processing may makes some post-processing code in examples not compatible.
I do not see the issue since the force chain feature has its own output name and the "postprocess_data" name seems ok to discribe the "almost" raw data. I mean, this is mostly averaged values by cell (velocities, granular temperature) or output of data (subdomain, mobility status).
Do you have suggestion about new names?
I agree with the tiny annoying capital letter tho x)