[DOC] Update the k-NN documentation to reflect the new Default values for K-NN engine hyper parameters

[navneet1v]

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With the changes merged for this GH issue: opensearch-project/k-NN#1354, we have updated the default values for the hyper parameters for K-NN engines(faiss, Lucene, Nmslib).

The changes are BWC, means that all the new indices that will be created will have the newer values and all the old indices will still reflect use the old values of the hyper parameters.

New Values

Parameters	Default Value
M	16
ef_construction	100
ef_search	100

Old Values

Parameters	Default Value
M	16
ef_construction	512
ef_search	512

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.

[navneet1v]

PR raised. #6272