Fix search-replica routing fairness and add VSCO 3.8.0 image publish workflow

[ossianpe]

Summary

• Fix search-replica preference fairness in IndexShardRoutingTable.filterAndOrderShards: filter matching replicas first, then shuffle/order, so writer replicas no longer bias which search copy is preferred.
• Add regression tests for fair split between search replicas when writable data replicas are present, and for ignoring writer replicas.
• Add .github/workflows/vsco-publish-opensearch-image.yaml to build a non-snapshot patched :server jar, validate it against upstream tag 3.8.0, and swap it into the official multi-arch base image (avoids full recompile).
• Harden the publish workflow: fetch the upstream 3.8.0 tag for the jar-swap safety check, build with -Dbuild.snapshot=false, and locate/verify the core jar by content rather than a hard-coded path.
• Branch also carries cherry-picks from the 3.8.0 release line (regexp/simple_query_string DoS bounds, OTEL alignment, bundled JDK, release notes, m2 mirror).

Test plan

• Run IndexShardRoutingTableTests (esp. search-replica fairness / writer-ignored cases)
• Trigger vsco-publish-opensearch-image (or dry-run locally) and confirm a single non-SNAPSHOT opensearch-3.8.0.jar is found and contains IndexShardRoutingTable
• Deploy/smoke the published image and confirm search traffic spreads across search replicas when writer replicas exist

Please note, the bulk of the files here are for getting helm operator releases working

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