Drop basic/org workflows, standardize on enhanced

[lkubb]

Drop org workflows

We decided we want to migrate away from the centralized (reusable) workflows in https://github.com/salt-extensions/central-artifacts for several reasons:

• We want/need to use Trusted Publishing to limit blast radius inside the organization, which currently does not work with reusable workflows from outside the repository. It does however work with reusable workflows from within. We still need to think about how to implement this exactly.
• Maintaining the centralized and the enhanced workflows is duplicate work. The centralized ones were intended to ensure automatically updating CI, but this is achieved via Copier as well.
• Some extensions require specific setup, such as saltext-vault relying on the vault CLI to be available for testing. We cannot account for each requirement the way it's dealt with right now. Extension maintainers might also want to modify their CI in some way, which only works with workflows inside their repository.

Drop basic workflows

The basic workflows are a relict from the deprecated create-salt-extension tool. Let's drop them as well, they are strictly inferior to the enhanced ones.

Enforce supported Salt/Python versions only

Since the test matrices are autogenerated by the template, we additionally need to ensure the inputs (salt_version, max_salt_version, python_requires) are updated automatically when Salt releases are released or EOL'd.

Note: The version logic might need to be updated in the future since 3007 could be EOL'd before 3006 is.