rust/pv: Support for writing data in PEM format

Use existing OpenSSL functionalities to create PEM files containing
arbitrary data.

Acked-by: Marc Hartmayer <marc@linux.ibm.com>
Acked-by: Christoph Schlameuss <schlameuss@linux.ibm.com>
Signed-off-by: Steffen Eiden <seiden@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

rust/pv/src/error.rs

@@ -106,6 +106,9 @@ pub enum Error {
     )]
     AddDataMissing(&'static str),
 
+    #[error("An ASCII string was expected, but non-ASCII characters were received.")]
+    NonAscii,
+
     // errors from other crates
     #[error(transparent)]
     PvCore(#[from] pv_core::Error),