feat: add experimental_personalization_api_key feature to RoFeatures

- Add MEILI_EXPERIMENTAL_PERSONALIZATION_API_KEY environment variable
- Add experimental_personalization_api_key field to Opt struct with CLI and env support
- Add experimental_personalization_api_key field to InstanceTogglableFeatures
- Store personalization API key in FeatureData for access through IndexScheduler
- Add experimental_personalization_api_key() method to IndexScheduler
- Update analytics destructuring to include new field
- Maintain RoFeatures Copy trait while properly handling Option<String>

crates/index-scheduler/src/features.rs

@@ -25,6 +25,7 @@ pub(crate) struct FeatureData {
     persisted: Database<Str, SerdeJson<RuntimeTogglableFeatures>>,
     runtime: Arc<RwLock<RuntimeTogglableFeatures>>,
     network: Arc<RwLock<Network>>,
+    experimental_personalization_api_key: Option<String>,
 }
 
 #[derive(Debug, Clone, Copy)]
@@ -188,7 +189,12 @@ impl FeatureData {
 
         let persisted_features: RuntimeTogglableFeatures =
             runtime_features_db.get(wtxn, db_keys::EXPERIMENTAL_FEATURES)?.unwrap_or_default();
-        let InstanceTogglableFeatures { metrics, logs_route, contains_filter } = instance_features;
+        let InstanceTogglableFeatures {
+            metrics,
+            logs_route,
+            contains_filter,
+            experimental_personalization_api_key,
+        } = instance_features;
         let runtime = Arc::new(RwLock::new(RuntimeTogglableFeatures {
             metrics: metrics || persisted_features.metrics,
             logs_route: logs_route || persisted_features.logs_route,
@@ -204,6 +210,7 @@ impl FeatureData {
             persisted: runtime_features_db,
             runtime,
             network: Arc::new(RwLock::new(network)),
+            experimental_personalization_api_key,
         })
     }
 
@@ -234,6 +241,10 @@ impl FeatureData {
         RoFeatures::new(self)
     }
 
+    pub fn experimental_personalization_api_key(&self) -> Option<&String> {
+        self.experimental_personalization_api_key.as_ref()
+    }
+
     pub fn put_network(&self, mut wtxn: RwTxn, new_network: Network) -> Result<()> {
         self.persisted.remap_data_type::<SerdeJson<Network>>().put(
             &mut wtxn,

crates/index-scheduler/src/lib.rs

@@ -886,6 +886,10 @@ impl IndexScheduler {
         self.features.features()
     }
 
+    pub fn experimental_personalization_api_key(&self) -> Option<&String> {
+        self.features.experimental_personalization_api_key()
+    }
+
     pub fn put_runtime_features(&self, features: RuntimeTogglableFeatures) -> Result<()> {
         let wtxn = self.env.write_txn().map_err(Error::HeedTransaction)?;
         self.features.put_runtime_features(wtxn, features)?;