Omit DORA chart from list of available visualizations

What does this MR do and why?

Removes the DORAChart from the list of available visualizations in the dashboard designer.

Screenshots or screen recordings

Before	After

How to set up and validate locally

To test this visually, you will need to setup the product analytics stack. But we can test this in a simpler way by querying the graphql endpoint for the list of visualizations.

# for the group at `groups/pa-snowplow-builtin` we pass just the group slug as the `fullPath`

{
  group(fullPath: "pa-snowplow-builtin") {
    customizableDashboardVisualizations {
      nodes {
        type
        slug
      }
    }
  }
}

Before	After

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #423427 (closed)