Backport PR #10899: Add undoManager to inserted cells (#10925)

Co-authored-by: Carlos Herrero <26092748+hbcarlos@users.noreply.github.com>

packages/shared-models/src/ymodels.ts

@@ -272,8 +272,7 @@ export class YNotebook
   insertCells(index: number, cells: YCellType[]): void {
     cells.forEach(cell => {
       this._ycellMapping.set(cell.ymodel, cell);
-      // cell.yawareness = this.yawareness;
-      // cell.yUndoManager = this.yUndoManager;
+      cell.undoManager = this.undoManager;
     });
     this.transact(() => {
       this.ycells.insert(
@@ -497,6 +496,13 @@ export class YBaseCell<Metadata extends models.ISharedBaseCellMetadata>
     return this.notebook ? this.notebook.undoManager : this._undoManager;
   }
 
+  /**
+   * Set the undoManager when adding new cells.
+   */
+  set undoManager(undoManager: Y.UndoManager | null) {
+    this._undoManager = undoManager;
+  }
+
   /**
    * Undo an operation.
    */