sampling

Is your feature request related to a problem? Please describe.
Even after the useful PR GeomScale/volesti#190 some examples are still failing to compile.

Describe the solution you'd like
Some have an easy fix e.g. vpolytope-volume while some other e.g. EnvelopeProblemSOS need some work to fix the cmake (at least in my Ubuntu 20.04 with gcc version `9.3

When writing data with qbeast format, the user needs to specify every time the columnsToIndex or cubeSize. This is ok if you want to change them, but it shouldn't be always explicit.

For example, if the user wants to append data to an existing table and maintain the same configuration, it should be able to write:

df.write.format("qbeast").save("existing-path")

instead