VC store for subspaces

[SimoneZaza]

Description

As a user, I also want this nice invite vc experience on subspace level!

Acceptance criteria

• Reuse "vc store" from space level
• Think it through: what about the ability to directly add vcs that are already in a space; what privileges does the user need to have to add external vcs to subspace (and thus to space); vcs from account can be directly added on space level, but not on subspace if they're not yet in the space, etc.

Additional Context

Functionality to reuse vc invite dialog to space for subspace was explored in #7334

Areas that will be affected

To be added during the refinement