docs: Update project-overview diagrams for the Hub CRD reference

Remove the crddocs repository box from page 2 of the embedded draw.io
source in all three project-overview SVGs, relabel crds.stackable.tech
to hub.stackable.tech and connect the operator repositories directly to
it (the Hub ingests the CRDs, Netlify only serves the docs site).

Only project-overview-documentation.drawio.svg renders that page, so
the other two files change only in their embedded source.

Author: lfrancke