Log if pipeline creation limit might be exceeded

What does this MR do and why?

Previously if a user pushed more than 4 refs to a pipeline, the PostReceive Sidekiq job would pick the first 4 and ignore the rest. This commit adds a log message to warn the admin this might be happening. Note that we can't be sure if a given ref would actually have a pipeline created for it since the CI rules would need to be evaluated to determine that.

Sample log message:

{
  "severity": "INFO",
  "time": "2024-03-18T22:42:14.742Z",
  "correlation_id": "01HS9VNFSWXCKJH0W0NDCK5WNV",
  "meta.caller_id": "PostReceive",
  "meta.remote_ip": "127.0.0.1",
  "meta.feature_category": "source_code_management",
  "meta.user": "root",
  "meta.user_id": 1,
  "meta.project": "root/go-micro-test",
  "meta.root_namespace": "root",
  "meta.client_id": "user/1",
  "meta.root_caller_id": "POST /api/:version/internal/post_receive",
  "message": "Some pipelines may not have been created because ref count exceeded limit",
  "ref_limit": 4,
  "total_ref_count": 5,
  "possible_omitted_refs": [
    "refs/tags/test9"
  ],
  "possible_omitted_ref_count": 1
}

Relates to #350886

How to set up and validate locally

1. Check out this branch.
2. Restart Sidekiq: gdk restart rails-background-jobs
3. Clone a project.
4. Create 5 tags or branches.
5. Run git push --all.
6. application_json.log should have that message.