Refactor slot status notification to decouple from accounts notifications (#21308)

Problem

Slot status can be used of in other scenarios in addition to account information such as transactions, blocks. The current implementation is too tightly coupled.

Summary of Changes

Decouple the slot status notification from accounts notification. Created a new slot status notification module.

accountsdb-plugin-interface/src/accountsdb_plugin_interface.rs

@@ -79,21 +79,36 @@ pub trait AccountsDbPlugin: Any + Send + Sync + std::fmt::Debug {
     fn on_unload(&mut self) {}
 
     /// Called when an account is updated at a slot.
+    #[allow(unused_variables)]
     fn update_account(
         &mut self,
         account: ReplicaAccountInfoVersions,
         slot: u64,
         is_startup: bool,
-    ) -> Result<()>;
+    ) -> Result<()> {
+        Ok(())
+    }
 
     /// Called when all accounts are notified of during startup.
-    fn notify_end_of_startup(&mut self) -> Result<()>;
+    fn notify_end_of_startup(&mut self) -> Result<()> {
+        Ok(())
+    }
 
     /// Called when a slot status is updated
+    #[allow(unused_variables)]
     fn update_slot_status(
         &mut self,
         slot: u64,
         parent: Option<u64>,
         status: SlotStatus,
-    ) -> Result<()>;
+    ) -> Result<()> {
+        Ok(())
+    }
+
+    /// Check if the plugin is interested in account data
+    /// Default is true -- if the plugin is not interested in
+    /// account data, please return false.
+    fn to_notify_account_data(&self) -> bool {
+        true
+    }
 }