Add frontend fixtures for releases

What does this MR do?

Adds a frontend fixture that represents the response of a call to get a single release object from the Release REST API.

The generated fixture is written to tmp/tests/frontend/fixtures-ee/api/releases/release.json and looks like this:

{
  "name": "The first release",
  "tag_name": "v1.1",
  "description": "Best. Release. **Ever.** :rocket:",
  "description_html": "<p data-sourcepos=\"1:1-1:33\" dir=\"auto\">Best. Release. <strong>Ever.</strong> <gl-emoji title=\"rocket\" data-name=\"rocket\" data-unicode-version=\"6.0\">🚀</gl-emoji></p>",
  "created_at": "2018-12-03T00:00:00.000Z",
  "released_at": "2018-12-10T00:00:00.000Z",
  "author": {
    "id": 3,
    "name": "John Doe4",
    "username": "user3",
    "state": "active",
    "avatar_url": "https://www.gravatar.com/avatar/2c75f98f3ea6cd6ee75cfbdfbb031388?s=80&d=identicon",
    "web_url": "http://localhost/user3"
  },
  "commit": {
    "id": "b83d6e391c22777fca1ed3012fce84f633d7fed0",
    "short_id": "b83d6e39",
    "created_at": "2016-09-27T14:37:46.000+00:00",
    "parent_ids": [
      "1b12f15a11fc6e62177bef08f47bc7b5ce50b141",
      "498214de67004b1da3d820901307bed2a68a8ef6"
    ],
    "title": "Merge branch 'branch-merged' into 'master'",
    "message": "Merge branch 'branch-merged' into 'master'\r\n\r\nadds bar folder and branch-test text file to check Repository merged_to_root_ref method\r\n\r\n\r\n\r\nSee merge request !12",
    "author_name": "Job van der Voort",
    "author_email": "job@gitlab.com",
    "authored_date": "2016-09-27T14:37:46.000+00:00",
    "committer_name": "Job van der Voort",
    "committer_email": "job@gitlab.com",
    "committed_date": "2016-09-27T14:37:46.000+00:00",
    "web_url": "http://localhost/namespace1/releases-project/-/commit/b83d6e391c22777fca1ed3012fce84f633d7fed0"
  },
  "upcoming_release": true,
  "milestones": [
    {
      "id": 2,
      "iid": 2,
      "project_id": 1,
      "title": "12.4",
      "description": null,
      "state": "active",
      "created_at": "2020-09-23T23:20:17.245Z",
      "updated_at": "2020-09-23T23:20:17.245Z",
      "due_date": "2019-02-10",
      "start_date": "2019-01-10",
      "expired": false,
      "web_url": "http://localhost/namespace1/releases-project/-/milestones/2",
      "issue_stats": {
        "total": 4,
        "closed": 1
      }
    },
    {
      "id": 1,
      "iid": 1,
      "project_id": 1,
      "title": "12.3",
      "description": null,
      "state": "active",
      "created_at": "2020-09-23T23:20:17.220Z",
      "updated_at": "2020-09-23T23:20:17.220Z",
      "due_date": "2019-01-10",
      "start_date": "2018-12-10",
      "expired": false,
      "web_url": "http://localhost/namespace1/releases-project/-/milestones/1",
      "issue_stats": {
        "total": 5,
        "closed": 3
      }
    }
  ],
  "commit_path": "/namespace1/releases-project/-/commit/b83d6e391c22777fca1ed3012fce84f633d7fed0",
  "tag_path": "/namespace1/releases-project/-/tags/v1.1",
  "assets": {
    "count": 6,
    "sources": [
      {
        "format": "zip",
        "url": "http://localhost/namespace1/releases-project/-/archive/v1.1/releases-project-v1.1.zip"
      },
      {
        "format": "tar.gz",
        "url": "http://localhost/namespace1/releases-project/-/archive/v1.1/releases-project-v1.1.tar.gz"
      },
      {
        "format": "tar.bz2",
        "url": "http://localhost/namespace1/releases-project/-/archive/v1.1/releases-project-v1.1.tar.bz2"
      },
      {
        "format": "tar",
        "url": "http://localhost/namespace1/releases-project/-/archive/v1.1/releases-project-v1.1.tar"
      }
    ],
    "links": [
      {
        "id": 2,
        "name": "Runbook",
        "url": "https://example.com/runbook",
        "direct_asset_url": "http://localhost/namespace1/releases-project/-/releases/v1.1/binaries/awesome-app-1",
        "external": true,
        "link_type": "runbook"
      },
      {
        "id": 1,
        "name": "linux-amd64 binaries",
        "url": "https://downloads.example.com/bin/gitlab-linux-amd64",
        "direct_asset_url": "http://localhost/namespace1/releases-project/-/releases/v1.1/binaries/linux-amd64",
        "external": true,
        "link_type": "other"
      }
    ]
  },
  "evidences": [
    {
      "sha": "760d6cdfb0879c3ffedec13af470e0f71cf52c6cde4d",
      "filepath": "http://localhost/namespace1/releases-project/-/releases/v1.1/evidences/1.json",
      "collected_at": "2020-09-23T23:20:17.763Z"
    }
  ],
  "_links": {
    "self": "http://localhost/namespace1/releases-project/-/releases/v1.1",
    "merge_requests_url": "http://localhost/namespace1/releases-project/-/merge_requests?release_tag=v1.1&scope=all&state=opened",
    "issues_url": "http://localhost/namespace1/releases-project/-/issues?release_tag=v1.1&scope=all&state=opened",
    "edit_url": "http://localhost/namespace1/releases-project/-/releases/v1.1/edit"
  }
}