Move to Python 3.12

[stvnrlly]

Our applications currently run on Python 3.9. This will no longer be supported before too long, so we want to move to 3.12, the current stable release.

All 3 repositories will need this upgrade:

• notifications-api
• notifications-admin
• notifications-utils

While doing this, we want to change other pieces only if necessary to make this upgrade.

Implementation Sketch and Acceptance Criteria

We're going to start with the notifications-utils repo for this work because it's smaller in size and a dependency for the API and admin.

There is also some open work for utils already in place to help with this effort: @terrazoon has created a PR to replace the orderedset library with the ordered_set library instead. This is a necessary step as a part of the Python update, and there may be others like it in the future.

(There is a corresponding admin PR to update this dependency as well, however it will need to be updated to reference the right version of notification-utils once that update is complete.)

It's a bit unclear what actually has to happen, but I suspect the following steps to start with:

• Installing the newest version of Python 3.12 on to your system with pyenv
• Creating a new virtual environment with the 3.12 installation
• Updating pyproject.toml to reference Pythong 3.12 instead of 3.9.x
• Telling Poetry to use the new virtual environment
• Running make bootstrap to get all dependencies loaded and seeing if anything breaks
• Running the tests and seeing if anything breaks
• Running the application and seeing if anything breaks (if possible)

We should only update other dependencies as absolutely necessary for now. While it's tempting to update all-the-things, that will be difficult to debug should things not work correctly! Furthermore, we may have to take a step-wise approach to this, meaning we update from 3.9 to 3.10 first, then 3.10 to 3.11, and so on.

At a high level, what we need with this update are the following:

• Python is updated to 3.12; make note if we have to step through the previous versions first to get there
• The application runs correctly, or the library is loaded correctly as a dependency (in the case of notifications-utils)
• The tests all run and pass
• Any required dependency updates are accounted for

Security Considerations

• Python 3.9 is starting to approach critical updates only, and will soon be the oldest supported version in the Python Cloud Foundry Buildpack - we'd like to move ahead of this before we absolutely have to.
• Newer versions of Python contain additional enhancements and improvements; they're also required for working with things like the newer versions of OpenSSL, which are required for FIPS.