fix: upstream shared memory zone size

[y82]

In NGINX Plus 37.0 upstream shared memory zone, due to newly added histograms stats, we've stepped over into next slot size for the peer stats struct: from 1024 to 2048k. This PR reflects this change.

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[mtbChef]

Thanks, Yar. I think we need to update this page as well: https://docs.nginx.com/nginx/admin-guide/monitoring/live-activity-monitoring/

Also - are you sure that bumping from 64k to 2048k is necessary? My understanding was that the memory expansion meant that we needed another slab. I may be off here, but intuitively feels like this exponential increase isn't necessary. Would you mind checking with @route443 , in case you haven't yet?

Lastly, it would be good to add a warning into the release notes for 37.0 about the expanded memory need.

[russokj]

I thought I saw an algorithm for determining what the memory zone size should be for the upstream group based on the number of upstream servers. Is this not the case?
It's from this JIRA ticket (which I assume this MR is related to): https://jira.f5net.com/browse/TECHDOCS-5034