Report full size of Ci::Pipeline hierarchy trees

Four Merge Requests to address https://gitlab.com/gitlab-org/gitlab/-/issues/358075

Step	Merge Request
1	!95753 (merged) Rename pipeline hierarchy methods
2	!95756 (merged) Report full size of Ci::Pipeline hierarchy trees	👈 You are here
3	!95857 (merged) Broadly restrict downstream pipeline tree size
4	!97841 (merged) Enable pipeline hierarchy size limit by default

What does this MR do and why?

This MR changes the reported size of a Ci::Pipeline hierarchy to be the count of all pipelines in one tree, regardless of direct relationships or lineage.

By using #all_objects, we only count the single upstream and all downstreams of a given downstream pipeline. For example, a tree consisting of 1 root pipeline that directly creates 1000 downstream pipelines will be reported as 1000 pipelines with a hierarchy of size 2. Instead, we will now log 1,001 pipelines all with a hierarchy size of 1001.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.