test: Disable the disk allocation decider

[siegfriedweber]

Description

Disable the disk allocation decider in the tests

Otherwise the tests depend on the disk usage of the node and if the relative watermark set in cluster.routing.allocation.disk.watermark.high is reached then the security index could not be created even if enough disk space would be available:

[2025-09-03T15:22:34,713][WARN ][o.o.c.r.a.DiskThresholdMonitor] [opensearch-nodes-cluster-manager-0] high disk watermark [90%] exceeded on [1xEltDMGQsmsMMYUy_nMBA][opensearch-nodes-data-0][/stackable/opensearch/data/nodes/0] free: 134.8gb[7.2%], shards will be relocated away from this node; currently relocating away shards totalling [0] bytes; the node is expected to continue to exceed the high disk watermark when these relocations are complete

Part of #2

Definition of Done Checklist

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Author

• Integration tests passed (for non trivial changes)

Reviewer

• Code contains useful comments
• Code contains useful logging statements
• (Integration-)Test cases added
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• Changelog updated
• Cargo.toml only contains references to git tags (not specific commits or branches)

Acceptance

• Feature Tracker has been updated
• Proper release label has been added
• Links to generated (nightly) docs added
• Release note snippet added
• Add type/deprecation label & add to the deprecation schedule
• Add type/experimental label & add to the experimental features tracker

[labrenbe]

lgtm

[labrenbe]

lgtm