[DOC] Update k-NN plugin documentation to reflect AVX512_spr SIMD optimization update

[naveentatikonda]

What do you want to do?

• Request a change to existing documentation
• Add new documentation
• Report a technical problem with the documentation
• Other

Tell us about your request. Provide a summary of the request.
FAISS recently added a new build mode, avx512_spr, which enables the use of advanced AVX512 instructions available since Intel® Sapphire Rapids. These instructions include avx512_fp16, avx512_bf16, avx512_vpopcntdq, and many others. Some optimizations leveraging these instructions, such as speeding up Hamming distance evaluation for binary vectors, have already been implemented and merged. Additional optimizations are also in the pipeline. This PR enables K-NN to utilize this new avx512_spr build mode.

If the underlying system is an Intel® Sapphire Rapids or a newer-generation processor, avx512_spr binaries are generated. Otherwise, depending on the features available in the system and consistent with the existing implementation, avx512, avx2, or generic binaries may be generated.

Version: List the OpenSearch version to which this issue applies, e.g. 2.14, 2.12--2.14, or all.
2.19

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.
opensearch-project/k-NN#2404