Update helper text in space/subspace creation

[SimoneZaza]

Description

As a user, I want to see helper text that makes sense in the given context. Now Challenges have become Subspaces, many of the instructions don't make sense.

Acceptance criteria

• [ ] Update the translation file
• [ ] …

Additional Context

Screen shots / UX designs / data that are relevant.

Areas that will be affected

To be added during the refinement