[WIP] ConvneXT Models for Classification and Segmentation

[Aakanksha-Rana]

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Summary

This code will be a 3D adaptation of the recently proposed 2D ConvneXT.
Original convnext would be useful for classification task. We also aim to use the convext module for segmentation task.

Checklist

• I have added tests to cover my changes
• I have updated documentation (if necessary)

Acknowledgment

• I acknowledge that this contribution will be available under the Apache 2 license.