KnnVectorQueryBuilder support for allowUnmappedFields

[ghostspiders]

KnnVectorQueryBuilder does not respect the index.query.parse.allow_unmapped_fields index setting. update KnnVectorQueryBuilder support for allowUnmappedFields.
#106846

[elasticsearchmachine]

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[benwtrent]

I think the change looks good. Gonna get CI to test. Thank you @ghostspiders !

[benwtrent]

buildkite test this please

[benwtrent]

buildkite test this please

[benwtrent]

@elasticmachine update branch

[benwtrent]

buildkite test this please

[benwtrent]

@ghostspiders

There are multiple failures around the yaml tests:

./gradlew ':qa:mixed-cluster:v8.13.3#mixedClusterTest' -Dtests.class="org.elasticsearch.backwards.MixedClusterClientYamlTestSuiteIT" -Dtests.method="test {p0=search.vectors/45_knn_search_byte/Test nonexistent field}" -Dtests.seed=A52D9437EA192750 -Dtests.bwc=true -Dtests.locale=it-IT -Dtests.timezone=Africa/Mbabane -Druntime.java=21

is one example.

I am thinking that those tests need to adjusted with a version skip to ensure that they are only ran on older versions where we would fail on a non-existent field directly.

[ghostspiders]

@benwtrent I passed this yaml tests
`./gradlew ':qa:mixed-cluster:v8.9.2#mixedClusterTest' -Dtests.class="org.elasticsearch.backwards.MixedClusterClientYamlTestSuiteIT" -Dtests.method="test {p0=search.vectors/45_knn_search_byte/Test nonexistent field}" -Dtests.bwc=true -Druntime.java=21

[benwtrent]

buildkite test this please

[benwtrent]

@elasticmachine update branch

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buildkite test this please

[benwtrent]

buildkite test this please

[benwtrent]

buildkite test this please

[benwtrent]

@elasticmachine update branch

[benwtrent]

buildkite test this please

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