xbps.packages: handle forced xbps upgrade

[lemmi]

Describe the bug

When updates for xbps are available, they need to be installed first:

The 'xbps' package must be updated, please run `xbps-install -u xbps`

The way the xbps.packages operation is written, it's not possible to achieve this.

To Reproduce

• Wait for xbps updates.
• Try anything with xbps.packages or xbps.update

Expected behavior

• Ensure xbps is updated before any other operations are done.

[Fizzadar]

We can probably add a new fact to check for this before passing to the shared package install method, and call update if needed.