internal: introduce 'add new major version script'

[tpasternak]

Checklist

• [ ] I have filed an issue about this change and discussed potential changes with the maintainers.
• [ ] I have received the approval from the maintainers to make this change.
• [ ] This is not a stylistic, refactoring, or cleanup change.

Please note that the maintainers will not be reviewing this change until all checkboxes are ticked. See the Contributions section in the README for more details.

Discussion thread for this change

Issue number: <please reference the issue number or url here>

Description of this change