Allow a provider to declare that a document in a protected index is not a resource

[DarshitChanpura]

ResourceIndexListener.postIndex creates a sharing record for every document written to a protected index. The only discriminator available to a provider is typeField(), which selects between registered types on a shared index (ResourcePluginInfo.java:192-207). There is no way to declare that a document is not a resource at all.

.plugins-ml-model is the concrete case: it holds one document per model chunk (MLModelManager.java:1042-1047, IMMEDIATE refresh), so protecting the type creates a parentless sharing record per chunk every time a chunked local model is registered.

A plugin can work around it by stamping a discriminator on the resource document only and declaring that as typeField() — chunks then resolve to no provider and are skipped at ResourceIndexListener.java:76-86 — but that logs a WARN per skipped write, which reads as an error and is not one.

Requests:

1. A provider-level way to declare that a document in a protected index is not a resource.
2. Downgrade the "type is not declared as a protected type" warning for indices that legitimately hold non-resource documents.

Note for implementers: a presence check on a numeric field cannot reuse extractFieldFromIndexOp, which reads stringValue() / binaryValue() only (ResourcePluginInfo.java:154-167). chunk_number is mapped long.

[DarshitChanpura]

Consumer: opensearch-project/ml-commons#5027, which works around this with a typeField discriminator in the meantime.