Refactor the issuable's webhooks data architecture
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/15381#note_47379504:
This adds
total_time_spent
in the issuable's webhook payload'schange
hash. This change makes theto_hook_data
/hook_data
/execute_hooks
very ugly and I think this will need a refactor in the future, but since this was forgotten in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/14308, I thought let's just add it, and think about refactoring later.