Maintenance: Update dependencies and refresh OpenAPI spec tooling

[M0D1xD]

Hi maintainers,

I noticed that this repository has not received updates for a while and some parts of the tooling and dependencies appear outdated.

I'd like to contribute by:

• Checking compatibility with the current OpenAPI generator
• Improving the API specification where needed

Thanks!

[sherwinski]

Hi @M0D1xD,

Thanks for reaching out! Overall I think this is a good idea but will need to confer with the team first as there are some workflow considerations to make first. I'll keep this issue updated as I have more information.

[WillPoulson]

We're currently experiencing issues related to the openapi schema

OneSignal/onesignal-python-api#62

I'm happy to raise a PR but if it's likely to be covered in this work I'll leave it.