Allow manually setting borderColor/backgroundColor in ChartJS options

[blakeseufert]

In

frontend/src/components/entity/ha-chart-base.js

Line 388 in 8a88033

data.datasets[loopI].borderColor = colors[loopI].rgbString();

the borderColor and backgroundColor are manually set from values obtained through getColorList, meaning if borderColor or backgroundColor were set in the data properties, they are ignored.

It would be great to only override borderColor/backgroundColor if they are not already set.