Benchmarker: allow overwriting ConstraintWeights in the benchmark config per solver benchmark

<solverBenchmark>
    <name>First Fit</name>
    <constraintConfigurationOverwrite>
          <constraintWeight constraintName="Room unavailable timeslot">0hard/1000soft</>
          <constraintWeight constraintPackage="org.optaplanner.examples.foo.bar" constraintName="Room conflict">0hard/0soft</>
    </>
</>