Typo fix for link
Typo fix.
Fixes
### Api-Key-Protected sample
-See the [secure secret management guide](../guide/secure_secret_management.md) for instructions on how to use this function.
+See the [secure secret management guide](../../guide/secure_secret_management.md) for instructions on how to use this function.
When calling via the gateway pass the additional header "X-Api-Key", if it matches the `secret_api_key` value then the function will give access, otherwise access denied.
