Implement implicit conversion to a QUBO (and interpretation of results)

[garrison]

What is the expected enhancement?

In Qiskit Optimization, it is customary for an OptimizationAlgorithm to attempt to convert a problem to a QUBO if necessary, by invoking QuadraticProgramToQubo (see also the converter tutorial). However, QRAO requires the user to perform this conversion manually, in large part because the current explicit interface requires the problem to be in its final form before the QuantumRandomAccessOptimizer is even constructed (#9). Once this requirement is dropped, it would be nice to allow implicit conversion to QUBOs as well.

When closing this, we should also remove the corresponding usage note from the README.