[Filesystem] Keep executable permission when a file is copied

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | /
| License       | MIT
| Doc PR        | /

I made this PR in order to have the same behavior as the default `cp` unix command: permissions are not keep when copying a file at the exception of the execution flag (unless `-p` is passed to the command).