Make pipeline IDs project-wide

With $CI_PIPELINE_IID implemented in #3691 (closed) (note: IID, not ID) we have a natural per-project counter for pipelines. That's great.

That being said, it feels awkward to see pipeline ID number 18 million in my project, and job ID number 50 million. Most IDs - and by ID I mean what I can see in the URL - are per project. Issues, merge requests, environments. Every new project starts with issue #1 (closed) and MR !1 (closed). Not with #15391432 and !53928402. This is a case for pipelines and build IDs - and that is:

1. inconsistent
   • If per-project issue IDs are better, so are per-project pipeline IDs.
2. hard to talk about with the team
   • "hey, I think this was broken in pipeline number 32 but I fixed in 34" vs "hey, I think this was broken in pipeline number 15,123,456 but I fixed in 16,987,543"
3. looks weird
   • How the internals operate shouldn't dictate how IDs are presented to a user.

Goal: The very first pipeline to run in a new project should be of a "visible" ID = 1 and available at https://gitlab.com/GROUP/PROJECT/pipelines/1.

Extracted from #3691 (closed).