Add button to 404 page to bring user back to last accessible point

[SimoneZaza]

Description

As a user trying to access content (or a subspace) within a (sub)space that is private, I want to get informative feedback and a good way to continue from here

Acceptance criteria

• Add button on the 404 page to return to the last step in the "tree" that user has access to
• Update the text and maybe the visual to align with overall platform styling

Additional Context

Screen shots / UX designs / data that are relevant.

Areas that will be affected

To be added during the refinement