VC Creation - add documents callout to the knowledge step

[bobbykolev]

Description

As a user, I want to be able to directly upload documents in the 'Add Knowledge' part of the VC creation flow.

Acceptance criteria

• [ ] Multiple documents upload available under the posts option in Add Knowledge flow.
• [ ] Links/documents are collected in a single callout named "Initial Links and Documents" in the Body of Knowledge flow step in the subspace

Additional Context

Extracted from: https://github.com/alkem-io/client-web/issues/6603

User flow: https://alkem.io/building-alkemio-org/challenges/improvingtheusere-6400/collaboration/vccreateflowwith3typ

UI Designs: https://www.figma.com/design/gV8GGWh99QRKfM65lwedrE/Dashboard-Update?node-id=482-207&t=jCXmCypVZY8hWnEi-1

Areas that will be affected

To be added during the refinement