Allow variation in stroke color, width, and opacity with Gradio sketch input

[1jsingh]

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Is your feature request related to a problem? Please describe.
The current "sketch" inputs do not allow variation in stroke color, width, and opacity. This compatibility would allow for deploying gradio apps for a range of user-scribble based image synthesis and editing applications.

Describe the solution you'd like
Add support gradio sketch inputs to allow variation in stroke color, width and opacity.

Additional context
Please refer to https://github.com/1jsingh/paint2pix for an example app deployed with streamlit-drawable-canvas which performs image editing and synthesis from coarse user-scribbles. It would be great to have gradio support similar drawing capabilities to allow for a range of interactive image editing applications.

[HuangChiEn]

add eyes on this issue.
Also similar issue #2030

[pngwn]

@HuangChiEn This is being worked on along with all other Sketch related issues currently.