chore: add license identifier to project metadata

[mschoettle]

License scanning tools (such as the one used by GitLab) rely on the project metadata (made available via the PyPi API) to detect the license for a package.

Currently, license: null is returned.

This PR adds the license to the project metadata.

Checklist

• I acknowledge that all my contributions will be made under the project's license
• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the Contribution Guidelines and my PR follows them
• I have titled the PR appropriately
• I have updated my branch with the main branch
• I have added tests that prove my fix is effective or that my feature works
• I have added the necessary documentation about the functionality in the appropriate .md file
• I have added inline documentation to the code I modified

[tiwarishubham635]

LGTM!