Make map overlays use generic named slot collections instead of feature-named slots

Description

Similar to how we're using map-layer to render traffic markers and all flight paths, we should use the same mechanism to render all map overlay items

e.g. to define a map bottom right overlay, instead of:

<OverlayBottomRight
          topOffset={maxTopHeight}
          bottomOffset={fullBottomHeight}
        >
          <div className="flex flex-col items-end">
            <div className="flex flex-col gap-4 items-end">
              <SlotLoader name="map.overlay-button-follow" />
              <SlotLoader name="flight.annotations-overlay" />
              <SlotLoader name="traffic.unknown-traffic-overlay" />
            </div>
            {/* <WelcomeOverlay /> */}
          </div>
        </OverlayBottomRight>

we should do something like

<OverlayBottomRight>
  <SlotLoader name="map.overlay.bottom-right" collection />
</OverlayBottomRight>

and let plugins define their own map.overlay.bottom-right items that will be automatically added to the map

Scope

• Refactor map overlay slots to use a generic one instead of hardcoded feature-named ones