Add pipeline lists to graphql

What does this MR do?

This adds paginated fields to GraphQL's ProjectType and MergeRequestType to allow fetching pipelines for those resources.

The queries for those could look like this:

project(fullPath: $project_path) {
  pipelines(first: 2) {
    pageInfo {
      hasNextPage
      hasPreviousPage
    }
    edges {
      cursor
      node {
        id
        status
      }
    }
  }
}

The returned data would then look like this:

{
  "data": {
    "project": {
      "pipelines": {
        "pageInfo": {
          "hasNextPage": true,
          "hasPreviousPage": false
        },
        "edges": [
          {
            "cursor": "Nzc=",
            "node": {
              "id": "77",
              "status": "FAILED"
            }
          },
          {
            "cursor": "Njc=",
            "node": {
              "id": "67",
              "status": "FAILED"
            }
          }
        ]
      }
    }
  }

the pageInfo field contains whether or not the client should keep fetching pages. While the edges array contains information about the elements in the collection:

• cursor is a base64 encoded version of the field that is used for ordering (by default, the primary key).
• node contains the requested information about the resource.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conform by the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
  • Has been reviewed by a Database specialist
• Conform by the merge request performance guides
• Conform by the style guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/48469