layout

Is your feature request related to a problem? Please describe.
I don't think Theme UI should be opinionated on which SVGs should be used for the Radio & CheckBox components

Describe the solution you'd like
Probably an additional prop called customIcon maybe... based on which we could conditionally render the passed SVG icon otherwise we use the default icons?

**Describe alter

I followed the dashboard layout tutorial and following code fails as the config param is typed as (breakpoint: Breakpoint, config: Omit<TemporarySidebarConfig, 'id' | 'anchor' | 'variant' | 'hidden'>) => IEdgeSidebarRegistry; where the anchor is omitted

scheme.configureEdgeSidebar((builder) => {
  builder
    .create("uni