Refactor KVStore config override explanation

The documentation previously referred to a weakly defined function
`storage_configuration`, however, this function was replaced at some
stage by `kv_init_storage_config`. Refactor the explanation on how to
override the default configurations to reflect this. Also, remove
the snippet which was used to show the implentation of
`storage_configuration`.

Author: harrisonmutai-arm

storage/docs/Configuration/CONFIGURATION.md

@@ -223,7 +223,7 @@ If file system is not set, the default file system and block device are applied
 
 ### Configuration functions API
 
-Applications must call the function **storage_configuration()** to instantiate the required configuration. This function is defined as weak to allow the replacement of this function with a completely different implementation of the instantiation of components.
+Applications must call the function **kv_init_storage_config()** to instantiate the required configuration. This function is defined as weak to allow the replacement of this function with a completely different implementation of the instantiation of components.
 
 Below is a list of setup functions that `storage_configuration()` calls in each case, and their description: