rust/pv: Provide access for SecretList members

Adds getter for SecretList and SecretEntry.
Adds enum to represent secret types.
Add Iterator functionality for SecretList.

While at it, make the datatype of the capacity of the list transparent
for users.

Signed-off-by: Steffen Eiden <seiden@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

rust/pv/src/lib.rs

@@ -70,7 +70,7 @@ pub mod uv {
     };
     #[cfg(feature = "uvsecret")]
     pub use crate::uvsecret::{
-        secret_list::SecretList,
+        secret_list::{ListableSecretType, SecretEntry, SecretList},
         uvc::{AddCmd, ListCmd, LockCmd},
     };
 }