What this PR does

Support out-of-order exemplar ingestion in the CircularExemplarStorage. During ingestion, exemplars are appended to / discarded from the circular buffer as usual, but their position in the (doubly) linked list is controlled to maintain temporal ordering. Adding elements to the head or the tail of the linked list is trivial, adding elements in the middle requires us to find an insertion point, which is achieved by traversing the linked list. A back link was introduced (doubly linked list) which dramatically speeds up finding the insertion point (out-of-order exemplars lie usually very close to the newest exemplar).

TODO

• Benchmarks
• Flag to control exemplar out-of-order window (uncouple it from the sample out-of-order window)

Which issue(s) does the PR fix:

Closes #13577

Does this PR introduce a user-facing change?

[FEATURE] Circular exemplar buffer supports out-of-order exemplars.