samples: rust: debugfs: add example for blobs

samples: rust: debugfs: add example for blobs

Extend the Rust debugfs sample to demonstrate usage of binary file
support. The example now shows how to expose both fixed-size arrays
and dynamically sized vectors as binary blobs in debugfs.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Matthew Maurer <mmaurer@google.com>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>