Add created_at to job webhooks

Update docs and specs

changelogs/unreleased/232887-add-created_at-to-job-webhooks.yml

+---
+title: Add created_at to job webhooks
+merge_request: 56835
+author:
+type: changed

doc/user/project/integrations/webhooks.md

@@ -1297,6 +1297,7 @@ X-Gitlab-Event: Job Hook
   "build_name": "test",
   "build_stage": "test",
   "build_status": "created",
+  "build_created_at": "2021-02-23T02:41:37.886Z",
   "build_started_at": null,
   "build_finished_at": null,
   "build_duration": null,

lib/gitlab/data_builder/build.rb

@@ -26,6 +26,7 @@ module Gitlab
           build_name: build.name,
           build_stage: build.stage,
           build_status: build.status,
+          build_created_at: build.created_at,
           build_started_at: build.started_at,
           build_finished_at: build.finished_at,
           build_duration: build.duration,

spec/lib/gitlab/data_builder/build_spec.rb

@@ -19,6 +19,9 @@ RSpec.describe Gitlab::DataBuilder::Build do
     it { expect(data[:tag]).to eq(build.tag) }
     it { expect(data[:build_id]).to eq(build.id) }
     it { expect(data[:build_status]).to eq(build.status) }
+    it { expect(data[:build_created_at]).to eq(build.created_at) }
+    it { expect(data[:build_started_at]).to eq(build.started_at) }
+    it { expect(data[:build_finished_at]).to eq(build.finished_at) }
     it { expect(data[:build_allow_failure]).to eq(false) }
     it { expect(data[:build_failure_reason]).to eq(build.failure_reason) }
     it { expect(data[:project_id]).to eq(build.project.id) }