Merge pull request #24092 from Aser-Abdelfatah:GSoC_Support_GatherElements_ONNX

GSoC Add ONNX Support for GatherElements #24092

Merge with: https://github.com/opencv/opencv_extra/pull/1082
Adds support to the ONNX operator GatherElements [operator docs](https://github.com/onnx/onnx/blob/main/docs/Operators.md#GatherElements)
Added tests to opencv_extra at pull request https://github.com/opencv/opencv_extra/pull/1082

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [x] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [x] The feature is well documented and sample code can be built with the project CMake

modules/dnn/src/init.cpp

@@ -157,6 +157,7 @@ void initializeLayerFactory()
     CV_DNN_REGISTER_LAYER_CLASS(Arg,            ArgLayer);
     CV_DNN_REGISTER_LAYER_CLASS(Reciprocal,     ReciprocalLayer);
     CV_DNN_REGISTER_LAYER_CLASS(Gather,         GatherLayer);
+    CV_DNN_REGISTER_LAYER_CLASS(GatherElements, GatherElementsLayer);
     CV_DNN_REGISTER_LAYER_CLASS(LayerNormalization, LayerNormLayer);
     CV_DNN_REGISTER_LAYER_CLASS(Expand,         ExpandLayer);