Update djangorestframework dependency

[murtazox04]

The current version constraint for the djangorestframework dependency in the payme-pkg package is too specific and may cause compatibility issues for projects requiring different versions of djangorestframework.

To address this, I've updated the requirements.txt file to use a broader version constraint:
djangorestframework>=3.14.0,<3.16.0

This change should allow the payme-pkg package to work with djangorestframework version 3.14.0 and higher, including newer versions like the one required by my project (^3.15.1), while maintaining compatibility for existing users.

Additionally, it might be beneficial to consider the following improvements:

1. Make the djangorestframework dependency version configurable: Introduce a configuration option or setting that allows users to specify the desired version of djangorestframework based on their project requirements.

2. Use environment variables for dependency versions: Implement support for setting the required djangorestframework version using environment variables. This would provide more flexibility for users with different project requirements and deployment environments.

3. Improve dependency management: Explore more robust dependency management solutions, such as using a tool like Poetry or pipenv, which can handle dependency resolution and versioning more effectively.

I've tested the updated package locally with the broader djangorestframework dependency constraint, and it seems to work correctly. However, thorough testing across different project configurations and djangorestframework versions would be recommended before merging these changes.

Please review the proposed changes and let me know if you have any concerns or suggestions for further improvements.