Add kNN search C++ examples

[Alexsandruss]

Description

Copies of examples/daal/cpp_sycl/source/k_nearest_neighbors/bf_knn_dense_search_batch.cpp:

• KDTree k-Nearest Neighbors search C++ example
• Brute force k-Nearest Neighbors search C++ example

[SmirnovEgorRu]

@Mergifyio rebase

[mergify[bot]]

Command rebase: success

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[SmirnovEgorRu]

/intelci: run

[Alexsandruss]

Example should be minimal. If you want to show both, why we need 2 examples instead of 1?

Formally, it's not in scope of this PR, but I removed classification part in search examples except label loading.

[Alexsandruss]

http://intel-ci.intel.com/eb69f561-0085-f106-af7e-8cdcd4b723a1

[mergify[bot]]

rebase

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