[Dashboard designer] Fetch available visualisations from backend

Problem to solve

Currently the dashboard designer only fetches a list of Jitsu compatible visualizations.

Note: The editor is hidden behind a combined_analytics_dashboards_editor feature flag.

Proposed solution

Update the frontend to fetch the list of available snowplow visualisations from the backend Create visualizations GraphQL endpoint (#411597 - closed). This feature does not have to be compatible with Jitsu dashboards because it is behind an additional feature flag.

Implementation plan

frontend 2️⃣

1. Update analytics_dashboard.vue
   • Replace the loadAvailableVisualizations() method with a GraphQL query that fetches the visualizations.
   • Only run the query when a dashboard has successfully been loaded or a new one is being created.
2. If a user clicks on one, add the selected visualization object to the dashboard in a new panel.
   • Note: Use the full object instead of a reference.
3. Verify the lists load Snowplow visualizations that can be added to a dashboard. (Saving does not work yet)
4. Update specs.