[Dashboard designer] Custom visualizations not fetched from correct location

Summary

Now that available snowplow visualizations are being loaded (Update analytics dashboard available visualizat... (!125278 - merged)) it seems the backend has a small issue where it looks in the current project for custom visualizations instead of the dashboard pointer project..

Steps to reproduce

1. Be on this MR: !125278 (merged)
2. Add a custom visualization to your dashboard pointer project
3. Visit the dashboard designer

500 error in the graphql query for visualizations.