Add missing GraphQL data for pipeline detail header

What does this MR do and why?

This MR aims to add the data provided by Rails and the Rest API to the GraphQL API in order to ensure that there is one single source of truth for the Frontend.

In this MR the following changes have been made:

• Introduce PipelineFlagsType to group pipeline's flag data in a specific field
• Introduce an EE module for the PipelineFlagsType which contains an EE-specific field
• Introduce a new method in the PipelineSerializer to only fetch the fields under the flags attribute
• Introduce PipelineFlagsResolver in order to define where the flag data will be fetched from by the PipelineFlagsType
• Add new fields to the PipelineType

Screenshots or screen recordings

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Before	After

How to set up and validate locally

1. Start up Gitlab locally
2. Find a Pipeline that you want to query from the Rails console and get its' iid as well as the project's full_path
3. Open GraphiQL explorer and query the pipeline's newly added fields

Example query:

{
  project(fullPath: "toolbox/gitlab-smoke-tests") {
    id
    pipeline(iid: 1) {
      # new fields
      name
      totalJobs
      triggeredByPath
      child
      latest
      failed
      refText
      source
      computeMinutes
      flags {
        cancelable 
      	failureReason  
      	retryable
        stuck
        yamlErrors
        latest
      }
      mergeRequest {
        sourceBranch
        targetBranch
      }
    }
  }
}

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 #411452 (closed)