Add gRPC supports for Search foundation; match-all query

[dayana-j]

Description

This PR adds gRPC support for Search for the opensearch-java client, starting with the match_all query type. It follows the same architecture pattern used for the Bulk gRPC transport.

The SearchRequestConverter converts the opensearch-java SearchRequest to the protobuf SearchRequest used by the gRPC SearchService. Currently only match_all is implemented:

private static org.opensearch.protobufs.MatchAllQuery convertMatchAll(MatchAllQuery matchAll) {
    org.opensearch.protobufs.MatchAllQuery.Builder builder =
        org.opensearch.protobufs.MatchAllQuery.newBuilder();
    if (matchAll.boost() != null) {
        builder.setBoost(matchAll.boost().floatValue());
    }
    return builder.build();
}

Other query types supported by the server (term, match, bool, range, k-NN, etc.) are not yet supported in this version and will throw an UnsupportedOperationException directing users to REST:

throw new UnsupportedOperationException(
     "Query type '" + query._kind() + "' is not yet supported for gRPC transport in this version. "
         + "Use REST transport for this query type."
 );

The SearchResponseConverter converts the protobuf SearchResponse back to the opensearch-java SearchResponse. This includes full response metadata (took, timed_out, _shards), hits metadata (total, max_score), and per-hit fields. Document _source is deserialized from raw bytes to the user's target class via the JsonpMapper:

static <TDocument> TDocument deserializeSource(
    byte[] sourceBytes, JsonpMapper jsonpMapper, Class<TDocument> tDocumentClass
) {
    InputStream stream = new ByteArrayInputStream(sourceBytes);
    jakarta.json.stream.JsonParser parser = jsonpMapper.jsonProvider().createParser(stream);
    parser.next();
    return jsonpMapper.deserialize(parser, tDocumentClass);
}

Unit tests cover the request conversion for match_all with various parameters and verify that unsupported query types throw appropriately. Integration tests index documents via gRPC bulk, then search with match_all over gRPC and verify the full response.

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[reta]

Thanks @dayana-j , I think this change needs a bit more thoughts:

• the GRPC transport support is strictly endpoint base (for now), however the _search is limited to only match_all query (it is not enough to filter endpoint, we need params or/and payload)
• the hybrid transport does internal routing based on endpoints as well, so we basically end up with the situation that user could only invoke match_all like queries even if REST based transport supports everything else

That would significantly limit its applicability I believe. The suggestion I have is to enhance endpoint support with request argument GrpcTransport.isEndpointSupported(endpoint, request) so the GRPC transport could check endpoint and perform the request conversion (yes, could be a bit wasteful work but at least we will properly route to REST transport till all queries are covered).

Curious WDYT? Thank you.