Default None ohttp_keys in Config::builder(

Without this, the configuration may fail when deserialization parses an empty string

Author: DanGould

payjoin-cli/ohttp-keys

@@ -73,7 +73,8 @@ impl AppConfig {
                 "ohttp_relay",
                 matches.get_one::<Url>("ohttp_relay").map(|s| s.as_str()),
             )?
-            .set_default("pj_directory", "https://payjo.in")?;
+            .set_default("pj_directory", "https://payjo.in")?
+            .set_default("ohttp_keys", None::<String>)?;
 
         let builder = match matches.subcommand() {
             Some(("send", _)) => builder,