Fix import of GlHoverLoadDirective and GlResizeObserver in stories

When running yarn start, the following warnings are printed:

WARN export 'default' (imported as 'GlHoverLoadDirective') was not found in './hover_load' (possible exports: DELAY_ON_HOVER, HoverLoadDirective)
WARN export 'default' (imported as 'GlHoverLoadDirective') was not found in './hover_load' (possible exports: DELAY_ON_HOVER, HoverLoadDirective)
WARN export 'default' (imported as 'GlResizeObserver') was not found in './resize_observer' (possible exports: GlResizeObserverDirective)
WARN export 'default' (imported as 'GlResizeObserver') was not found in './resize_observer' (possible exports: GlResizeObserverDirective)

Seems like the stories try to import default.

Task: Update to named imports