Extend the existing mentions of NVS examples with 2 newly added `nvs_statistics` and `nvs_iteration`.
Add a new example showcasing iterating over NVS entries of a specific (or any) type, and the info to be obtained from therein.
Add a new example showcasing how to obtain and interpret statistics about the usage of an NVS partition. Also demonstrates how stats change after writing some key-value pairs in 2 separate namespaces.