In the pipeline message, the duration of the pipeline was shown as:

> gitlab-org/gitlab-ee: Pipeline #8002259 of master branch by Douwe Maan
failed in 8612 seconds

But this many seconds only gave me a clue how long the pipeline took,
so now this will be shown as something like: 02:20:12 which gives a much
better measure of time.

Pipelines triggered from API don't have a corresponding
user, so we show that it's from API, same as from the
web UI

Closes #25609

rather than using SHA for the pipeline link.

Also add Service#event_names so that we don't have to hard code all
event names in ServiceParams. Note that I don't know why we want to
call plural on issue_event and merge_request_event so that we still
need to hard code them for issues_event and merge_requests_event.
See app/helpers/services_helper.rb for those special rules.