Add the possibility to take a folder in input

[JulienPercheron]

Currently, the app only takes a single las/laz file in input, thus making it tedious to work with multiple files.

The app could benefit from the option of giving it a folder in input. The process would then be applied to all the las/laz files inside that folder.

Note: currently the output filename cannot be given. Only the output folder name can be specified (because the output is constituted by a bunch of files that we need to regroup by means of a folder (the ouput one). This means that when iterating on the files of some input folder one needs the export folder must also be changed in order for the multiple runs to NOT overwrite their results. Hence solving this issue is a bit more complicated than looping on the input files

Moreover, the Docker image (and its documentation) would need to be changed too in order to support the specification of an input folder.