lift restriction on 'component' in 'package-repositories' properties of config

[Dan Ryan]

Currently, when adding a `package-repositories` section to a `.launchpad.yaml`, the `component` argument only accepts one of `main`, `restricted`, `universe`, or `multiverse`.

This is only a valid restriction when using the ubuntu archive, however, and is not guaranteed to be a valid restriction when for example attempting to add an additional package repository in this section of the config.

For example, we maintain a private repository with some cuda versions in it which use the following structure:

deb https://my-archive.com/ppa/cuda jammy cuda/12-2

In this case, the `component` would be: `component: [cuda/12-2]`

This is invalid though, because `cuda/12-2` is not one of the allowed components.

Based on our brief discussion at https://chat.canonical.com/canonical/pl/daf79d1d9prp9bbs46acmzitcr I am proposing that we lift the restriction here.

Thanks!