Include null values in DORA metrics API response

What does this MR do and why?

Include null values in DORA metrics API response

When a user selects date alongside DORA metrics on GraphQL we include placeholders with nil values for dates that do not have data. For example, assume that a Project/Group has the following DORA metrics:

{ date: 2023-06-15, DeploymentFrequency: 0.3 },
{ date: 2023-06-18, DeploymentFrequency: 0,7 }

After this MR, if a user selects DORA metrics from 2023-06-15 to 2023-06-18 the API will return:

{ date: 2023-06-15, DeploymentFrequency: 0.3 },
{ date: 2023-06-16, DeploymentFrequency: nil },
{ date: 2023-06-17, DeploymentFrequency: nil },
{ date: 2023-06-18, DeploymentFrequency: 0,7 }

This helps frontend to pass data between components. More information at #393464 (closed)

How to set up and validate locally

1. Run the following seed: FILTER=cycle_analytics SEED_VSA=1 bundle exec rake db:seed_fu
2. Take the project path from the seed output and use in the following GraphQL query:

The seed generates data for the last 100 days we need to adjust the query startDate to be before earlier than that in order to have some nil data filled:

 query doraForProject{
  project(fullPath: "PROJECT_PATH") {
 		dora {
      metrics(startDate: "2023-02-21", endDate: "2023-07-21") {
        date
        deploymentFrequency
        changeFailureRate
        timeToRestoreService
        leadTimeForChanges
      }
     }
   }
 }

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.