Core/DBLayer: Add QueueSize() method (#26733)

* Core/DBLayer: Add QueueSize() method

Add QueueSize() method to database objects (Login, Character and World) that returns how many tasks are queued.
Include the queue size of the 3 databases in ".server debug" command

* Make the code less threadsafe

* Send data to InfluxDB

* Update grafana dashboard

(cherry picked from commit 96dc110f4a)

src/server/database/Database/DatabaseWorkerPool.cpp

@@ -414,6 +414,12 @@ void DatabaseWorkerPool<T>::Enqueue(SQLOperation* op)
     _queue->Push(op);
 }
 
+template <class T>
+size_t DatabaseWorkerPool<T>::QueueSize() const
+{
+    return _queue->Size();
+}
+
 template <class T>
 T* DatabaseWorkerPool<T>::GetFreeConnection()
 {

src/server/database/Database/DatabaseWorkerPool.h

@@ -213,6 +213,8 @@ class DatabaseWorkerPool
 #endif
         }
 
+        size_t QueueSize() const;
+
     private:
         uint32 OpenConnections(InternalIndex type, uint8 numConnections);