Link preview and link bubble broken in public shares (and with `reference_opengraph = false`)

[mejo-]

Describe the bug
In public shares we currently don't load previews (or other reference widgets). Same if reference_opengraph is disabled in server configuration. This leads to several issues:

• Links that are configured to be displayed as previews don't get displayed at all
• Links to other pages in the same collective don't get rerouted but instead get opened in a new tab

To Reproduce
Steps to reproduce the behavior:

• Open a public share of a text file with links configured as link previews

Expected behavior

Some thoughts:

• I wonder whether we should limit the effect of disabling reference_opengraph to disable previews of external pages and still load references to other objects from the same Nextcloud instance.
• In public shares (or with reference_opengraph disabled) we have to display links to external pages as text links no matter what.

[juliusknorr]

As discussed in the call:

• Text: Let's enable the fallback for link previews in the preview node type
• Server: File a enhancement request for previews on public shares