Define snowplow built-in analytics dashboards

What does this MR do and why?

• Defines a new Audience and Behaviour analytics dashboard in YAML that uses a Snowplow-compatible schema.
• When the product_analytics_snowplow_support flag is enabled, every project will have both of these added to their list when querying the GraphQL API.

How to set up and validate locally

• Make sure you have an Ultimate licence working.
• Make sure the product analytics stack is set up.
• Call the list of dashboards for a project:

query {
  project(fullPath: "twitter/test-analytics-1") {
    name
    productAnalyticsDashboards {
      nodes {
        title
        panels {
          nodes {
            title
            visualization {
              type
              options
              data
            }
          }
        }
      }
    }
  }
}

• Note that there are no dashboards in the list.
• Enable the product_analytics_snowplow_support feature flag.
• Make the same call, and assert that there are two dashboards. One called Audience and one called Behaviour.
• It should also include any other dashboards defined for the project.
• These should include Cube queries that work with snowplow. (They should be referring to SnowplowTrackedEvents and SnowplowSessions.

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 #407397 (closed)