Update k-NN API specifications with 2.17 changes

[ryanbogan]

In OpenSearch 2.17, k-NN made changes to various APIs, which have not yet been reflected in the specifications. These changes include adding rescore and oversampling factor to a k-NN query, and adding mode and compression options during index creation and training models.

The API specifications need to be updated to be consistent with the current code in the k-NN repository.