Store: add failing test for proxy heap sorting issue

[mhoffm-aiven]

This test was created with production data from a user sent to me. It shows that despite getting sorted responses from store apis the end result of proxy heap is not sorted because of adverse store labels. The offender in this case is that receivers are not instructed to drop the "cluster" label so all series from the receivers are sorted before series from the store making them overall unsorted in the prometheu sense.

[mhoffm-aiven]

Store labels:
Receive labels:

[MichaHoffmann]

The test failure is intended to show the issue

[MichaHoffmann]

So i have a proposition how to solve all this:

• we should establish the invariant that store apis always respond with sorted series; to do that in first iteration we pipe all sends through "resortingServer" at first
• if we do it like that we can get rid of cuckoofilter stuff since we are ( at first ) always resorting to keep the invariant
• if we have the invariant that store responses are sorted we can just use whole labelset in proxy heap Less and end up sorted in the expected way always; thus solving the problem
• we can optimize the resorting away in some cases in followups if we can prove that the response is already sorted ( or still sorted after adding extlabels )

[mhoffm-aiven]

Continued in #6706