fix: Actually make feature flags use snake_case

The documentation already describes them as snake_case, so technically
this is a bug fix.

Author: tlater-famedly

src/config.rs

@@ -268,6 +268,7 @@ pub type Set<T> = Vec<T>;
 
 /// Opt-in features
 #[derive(Debug, Clone, Deserialize, PartialEq)]
+#[serde(rename_all = "snake_case")]
 pub enum FeatureFlag {
 	/// If SSO should be activated. It requires idpId, idpUserName, idpUserId
 	/// mapping

tests/environment/config.template.yaml

@@ -33,5 +33,5 @@ famedly:
   idp_id: @IDP_ID@
 
 feature_flags:
-  - SsoLogin
+  - sso_login
 cache_path: ./test