Merge pull request #24569 from Abdurrahheem:ash/padding_value_fix

Add support for custom padding in DNN preprocessing #24569

This PR add functionality for specifying value in padding.
It is required in many preprocessing pipelines in DNNs such as Yolox object detection model

### 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
- [ ] 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/include/opencv2/dnn/dnn.hpp

@@ -1212,7 +1212,7 @@ CV__DNN_INLINE_NS_BEGIN
         CV_WRAP Image2BlobParams();
         CV_WRAP Image2BlobParams(const Scalar& scalefactor, const Size& size = Size(), const Scalar& mean = Scalar(),
                             bool swapRB = false, int ddepth = CV_32F, DataLayout datalayout = DNN_LAYOUT_NCHW,
-                            ImagePaddingMode mode = DNN_PMODE_NULL);
+                            ImagePaddingMode mode = DNN_PMODE_NULL, Scalar borderValue = 0.0);
 
         CV_PROP_RW Scalar scalefactor; //!< scalefactor multiplier for input image values.
         CV_PROP_RW Size size;    //!< Spatial size for output image.
@@ -1221,6 +1221,7 @@ CV__DNN_INLINE_NS_BEGIN
         CV_PROP_RW int ddepth;   //!< Depth of output blob. Choose CV_32F or CV_8U.
         CV_PROP_RW DataLayout datalayout; //!< Order of output dimensions. Choose DNN_LAYOUT_NCHW or DNN_LAYOUT_NHWC.
         CV_PROP_RW ImagePaddingMode paddingmode;   //!< Image padding mode. @see ImagePaddingMode.
+        CV_PROP_RW Scalar borderValue;   //!< Value used in padding mode for padding.
     };
 
     /** @brief Creates 4-dimensional blob from image with given params.