Update file permissions (#2499)

## Issue Addressed

Resolves #2438 
Resolves #2437 

## Proposed Changes

Changes the permissions for validator client http server api token file and secret key to 600 from 644. Also changes the permission for logfiles generated using the `--logfile` cli option to 600.

Logs the path to the api token instead of the actual api token. Updates docs to reflect the change.

common/filesystem/src/lib.rs

@@ -52,7 +52,7 @@ pub enum Error {
     UnableToRemoveACLEntry(String),
 }
 
-/// Creates a file with `600 (-rw-------)` permissions.
+/// Creates a file with `600 (-rw-------)` permissions and writes the specified bytes to file.
 pub fn create_with_600_perms<P: AsRef<Path>>(path: P, bytes: &[u8]) -> Result<(), Error> {
     let path = path.as_ref();
     let mut file = File::create(&path).map_err(Error::UnableToCreateFile)?;