Upgrade elastiknn to 8.12.2.1

[alexklibisz]

Upgrading to the latest release which has some performance improvements. Still fine to keep this in disabled state as it's still slower than many alternatives.

I re-ran the containerized benchmark on an r6i.4xlarge and got these results:

Model	Parameters	Recall	Queries per Second
eknn-l2lsh	L=100 k=4 w=1024 candidates=500 probes=0	0.378	314.650
eknn-l2lsh	L=100 k=4 w=1024 candidates=1000 probes=0	0.446	247.659
eknn-l2lsh	L=100 k=4 w=1024 candidates=500 probes=3	0.634	258.834
eknn-l2lsh	L=100 k=4 w=1024 candidates=1000 probes=3	0.716	210.380
eknn-l2lsh	L=100 k=4 w=2048 candidates=500 probes=0	0.767	271.442
eknn-l2lsh	L=100 k=4 w=2048 candidates=1000 probes=0	0.846	221.127
eknn-l2lsh	L=100 k=4 w=2048 candidates=500 probes=3	0.921	199.353
eknn-l2lsh	L=100 k=4 w=2048 candidates=1000 probes=3	0.960	171.614

This is about 20% worse than the non-containerized benchmarks running on the same instance, reported here: alexklibisz/elastiknn@ddf637a. Not quite sure why the difference, but I don't have time to diagnose right now. If I had to speculate it's probably because the containerized version runs both ann-benchmarks and the elasticsearch server on one CPU, whereas non-containerized runs elastiknn container on one cpu and ann-benchmarks on the host.