Add sample parameter to control reject sampling crash

[fealho]

Problem Description

Add an argument to sample (e.g. graceful_reject_sampling), which would default to False, that controls whether it should crash if no rows can be sampled within a given number of iterations or just return them with a warning.

• If the user passes False (which would be the default) it would raise an exception like it currently does.
• If the user passes True, and if it is not possible to generate all the requested rows, it would just issue a warning and return whatever it was able to generate except in the case in which it was not able to generate any valid row at all, in which an exception would also be raised.