[FEATURE] allow to add border

[adbenitez]

Is your feature request related to a problem? Please describe. I would like to use this library to create stickers

Describe the solution you'd like allow to set a border_color parameter or "sticker" mode that would allow to set a white border contour

Describe alternatives you've considered using OpenCV instead as shown in this tutorial: https://withoutbg.com/resources/creating-sticker

Additional context the stickers are generated by a bot in a chat app and they need a white border