[CMSUI] Toolbar in public bundle #49

Describe the PLIP task

We need to show the CMSUI toolbar in the public bundle when logged in. It has to still be lazy loaded, and do not force the public bundle to rely on @plone/cmsui concourse. The toolbar also need to be configurable from the app bundle (customizations). We still have to leave the door open to people that would only want to deploy the public side of a site as standalone, no cmsui at all.

These restrictions alone make it a challenge.
We could use an iframe that calls the editor bundle and load the toolbar component in there.
Suggestions are welcomed.

Link to the parent PLIP
#3

Additional context

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