Allow for more map customization

[AhmeddNofal]

Hello, great job on making this flutter package!
I just thought it be even better if it allowed more map customization by exposing the GoogleMap widget parameters, making it possible to add polylines for example, as I currently didn't find any way to add polylines or polygons to the map using the widgets provided by the package.
if you would like to add a such feature I would be glad to help out : )