Add workload randomization

Currently, the configured reference and offset point sources are fixed as seen below:

const Direction test_reference_point{0.5, 0.1};
const Direction test_offset_point{test_reference_point.ra + 0.02,
                                  test_reference_point.dec + 0.02};

We want to generate these point at random (or fixed) when the benchmark user specifies so.