[docs] Update keystore location

With elastic#57856 the default keystore
location was moved from the data folder to the config folder to align
with other applications in the stack.  This updates the secure settings
docs to reference the correct location.

Closes elastic#111915

docs/setup/secure-settings.asciidoc

@@ -18,8 +18,8 @@ To create the `kibana.keystore`, use the `create` command:
 bin/kibana-keystore create
 ----------------------------------------------------------------
 
-The file `kibana.keystore` will be created in the directory defined by the
-<<path-data, `path.data`>> configuration setting.
+The file `kibana.keystore` will be created in the `config` directory defined by the
+environment variable `KBN_PATH_CONF`.
 
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 [[list-settings]]