UX: Add an icon to toggle/open the panel when in Canvas mode

[qq99]

Is your feature request related to a problem? Please describe

This panel:

has no obvious mechanism of opening for those unfamiliar with Storybook. It seems the only ways to open it are:

• Hit the A or D key (not discoverable, requires you to have already known these hotkeys)
• Find it in this ... (I didn't even think to click on this)
  

Describe the solution you'd like

If the panel applies to the Canvas tab, then I'd expect to see a small icon here with the other tools to improve discoverability

Maybe it could have some knobs/gears

Describe alternatives you've considered

N/A

Are you able to assist to bring the feature to reality?

Perhaps

Additional context

I work at Shopify, so this feature request is a request on behalf of myself & a few like-minded developers

┆Issue is synchronized with this Asana task by Unito

[MichaelArestad]

@shilman There is a current affordance for this:

After doing a bit more testing, there is a bug.

1. I open a story.
2. I make sure the addon panel is visible, a
3. I go to full screen mode, f
4. The addon panel and sidebar go away, but BOTH the buttons to get them back are not visible.

5. The icons reappear if I toggle the sidebar or addon individually, s or a