Add config prop

[curio77]

This way, a config object that might otherwise be passed to Plotly.setPlotConfig() or as the last argument to Plotly.newPlot(), can be passed to the Plotly Vue component. It is still possible to pass individial config props that get merged into the resulting config object, but using the new config prop allows for encapsulation of configuration as well as reuse and may help keep things tidier.