DeepRegNet/DeepReg

# Description

Please include a summary of the change and which issue is fixed. Please also include
relevant motivation and context. List any dependencies that are required for this
change.

Fixes #<issue_number>

## Type of change

What types of changes does your code introduce to DeepReg?

_Please check the boxes that apply after submitting the pull request._

- [ ] Bugfix (non-breaking change which fixes an issue)
- [ ] Code style update (formatting, renaming)
- [ ] Refactoring (no functional changes, no api changes)
- [ ] Documentation Update (fix or improvement on the documentation)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Other (if none of the other choices apply)

## Checklist

_Please check the boxes that apply after submitting the pull request._

_If you're unsure about any of them, don't hesitate to ask. We're here to help! This is
simply a reminder of what we are going to look for before merging your code._

- [ ] I have
      [installed pre-commit](https://deepreg.readthedocs.io/en/latest/contributing/setup.html)
      using `pre-commit install` and formatted all changed files. If you are not
      certain, run `pre-commit run --all-files`.
- [ ] My commits' message styles matches
      [our requested structure](https://deepreg.readthedocs.io/en/latest/contributing/commit.html),
      e.g. `Issue #<issue number>: detailed message`.
- [ ] I have updated the
      [change log file](https://github.com/DeepRegNet/DeepReg/blob/main/CHANGELOG.md)
      regarding my changes.
- [ ] I have added tests that prove my fix is effective or that my feature works
- [ ] I have added necessary documentation (if appropriate)