Apply ref_option lint findings (#7143)

Quote from the lint description:
"More flexibility, better memory optimization, and more idiomatic Rust code.

&Option<T> in a function signature breaks encapsulation because the caller must own T and move it into an Option to call with it. When returned, the owner must internally store it as Option<T> in order to return it. At a lower level, &Option<T> points to memory with the presence bit flag plus the T value, whereas Option<&T> is usually optimized to a single pointer, so it may be more optimal."

src/config.rs

@@ -1076,7 +1076,7 @@ fn validate_config(cfg: &ConfigItems, on_update: bool) -> Result<(), Error> {
 
         validate_internal_sso_issuer_url(&cfg.sso_authority)?;
         validate_internal_sso_redirect_url(&cfg.sso_callback_path)?;
-        validate_sso_master_password_policy(&cfg.sso_master_password_policy)?;
+        validate_sso_master_password_policy(cfg.sso_master_password_policy.as_ref())?;
     }
 
     if cfg._enable_yubico {
@@ -1271,7 +1271,7 @@ fn validate_internal_sso_redirect_url(sso_callback_path: &String) -> Result<open
 }
 
 fn validate_sso_master_password_policy(
-    sso_master_password_policy: &Option<String>,
+    sso_master_password_policy: Option<&String>,
 ) -> Result<Option<serde_json::Value>, Error> {
     let policy = sso_master_password_policy.as_ref().map(|mpp| serde_json::from_str::<serde_json::Value>(mpp));
 
@@ -1725,7 +1725,7 @@ impl Config {
     }
 
     pub fn sso_master_password_policy_value(&self) -> Option<serde_json::Value> {
-        validate_sso_master_password_policy(&self.sso_master_password_policy()).ok().flatten()
+        validate_sso_master_password_policy(self.sso_master_password_policy().as_ref()).ok().flatten()
     }
 
     pub fn sso_scopes_vec(&self) -> Vec<String> {