Allow host to customize the colors for user

Right now we have a naive logic to determine the color to be shown for a remote collaborator.

We should also allow the host to pass the color for the user and those colors can be used to render the remote pointer/selection and avatar.

Usecase If the host has some logic of assigning the colors then this will help the host to use the same when using Excalidraw in collab mode as well

Solution Add an attribute color under the user prop which will help host to control it

user: { 
  name: string,
  color: { backgroud: string, stroke: string }
}

EDIT since we don’t use user prop anywhere so we can pass color in collaborator when updating scene

cc @dwelle

[ad1992]

We could accept the avatarUrl as a prop and render it. Since this an addition of a new prop let’s track it as a separate issue. https://github.com/excalidraw/excalidraw/issues/2922

[ad1992]

closed via https://github.com/excalidraw/excalidraw/pull/2943