feat(DefaultRenderer): custom color

[rbalet]

Is your feature request related to a problem? Please describe.
To avoid having the recreate the renderer just to be ab le to change the color, letting user change those color while instantiating the class would be useful

Describe the solution you'd like
Add two color variable that can be set through class instantiation.

Additional context
The Idea

export class DefaultRenderer implements Renderer {
  underMeanColor: string
  overMeanColor: string

   constructor(underMeanColor = '#0000ff', overMeanColor = '#ff0000') {
     this.underMeanColor = underMeanColor
     this.overMeanColor = overMeanColor
     super() 
  } 
  
    public render( { count, position }: Cluster, stats: ClusterStats, map: google.maps.Map): Marker {
    // change color if this cluster has more markers than the mean cluster
    const color =
      count > Math.max(10, stats.clusters.markers.mean) ? this.overMeanColor : this.underMeanColor;
   
   // ...
}