[enhancement]: Support deb822 for `sources`

# Enhancement

The 'Apt Configure' module supports two keys which add repos:

* `sources`. According to https://cloudinit.readthedocs.io/en/latest/reference/modules.html#mod-cc-apt-configure, it allows users to add sources to different files.
* `sources_list`. According to https://cloudinit.readthedocs.io/en/latest/reference/yaml_examples/apt.html#example-1, it adds all sources to a single file.

So, it looks like there is **no way to add deb822 repos to different sources files**. Reading https://github.com/canonical/cloud-init/blob/main/cloudinit/config/cc_apt_configure.py#L435, I don't see any such logic.

This is problematic, as deb822 is the new way to add repos, and adding repos to multiple sources files is a perfectly legitimate use case.