Use jinja to render configurable templates

[ArBridgeman]

Summary

For setting the dependency manager version (poetry_version), default python version for a project (not set) and os_version, we should modify the templates to use jinja variables which are rendered before the files are written out.

To reduce stress, the output format should look roughly the same as what developers currently see. We do want to move the tbx workflow endpoints to nox as we need the noxconfig::PROJECT_CONFIG & don't want to expose it. Before doing something like that, let's mark all of them with deprecation warnings so we can 1) alert developers change is coming and 2) get feedback if endpoints we plan to just remove are actually needed.

This is helpful to do already as we are releasing a new PTB with the poetry_version bumped from 2.1.4 to 2.3.0. This has previously caused headaches for developers, so this allows them to override it until they have time to adjust it (<3 months).