Implemented method to add a task to firestore

lib/src/resources/firestore_provider.dart

@@ -46,6 +46,12 @@ class FirestoreProvider {
 
   //-------------------------Task related operations----------------------------
 
+  /// Adds a task to the tasks collection in firestore.
+  Future<void> addTask(TaskModel task) async {
+    final dataMap = task.toFirestoreMap();
+    await firestore.collection('tasks').add(dataMap);
+  }
+
   /// Returns a stream of [List<Task>]
   ///
   /// The [event] parameter is used to query tasks that are part of a certain