Set sparkline value to 0 if the metric is missing

What does this MR do and why?

Checks if the metric exists in the sparkline data. otherwise defaults to 0

Related to Exec Dashboard - Failing request for summary en... (#384551 - closed)

Screenshots or screen recordings

Before	After

How to set up and validate locally

Enable dashboard

1. Enable the dashboards page

   Feature.enable(:group_analytics_dashboards_page)

2. Ensure you're on the ultimate plan
3. Visit any Group > Analytics > Dashboards

Seed data

1. Create a project in the group
2. Create an environment from the UI named production
3. Open the rails console

   rails c

4. Find the environment id

   // Within the rails console
   $ e = Environment.order(:id)[-1]

5. Seed DORA daily metrics in the environment using the environment

   // Within the rails console
   $ 100.times { |i| Dora::DailyMetrics.create(environment_id: e.id, date: (i + 1).days.ago, deployment_frequency: rand(50), incidents_count: rand(5), lead_time_for_changes_in_seconds: rand(50000), time_to_restore_service_in_seconds: rand(100000)) }

Viewing the dashboard

Navigate to the the exec dashboard for the group and specify the project path in the `query parameter

// For example
// Group: flightjs
// Project: flightjs/flight
Navigate to http://gdk.test:3000/groups/flightjs/-/analytics/dashboards?query=flightjs/flight

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.