[feature request] add support for install-oem subcommand

[Olivier Gayot]

The `ubuntu-drivers list-oem` command can be used to list OEM meta-packages, which is great.

However, there seems to be no way to install listed OEM meta-packages without also pulling all the applicable third-party drivers - which is something that we want in subiquity.
`ubuntu-drivers install <oem-meta-package>` does not do the trick and reading the code, it seems intentional.

One could simply install the packages using apt-get install ; but then they don't get upgraded to their version in the OEM archive. Instead, one would need to run:

 * apt-get install <package> # To install the package from the Ubuntu archive
 * apt-get update <options ...> # To make the system aware of the OEM archive
 * apt-get install <package> # To upgrade the package to the version in the OEM archive

In subiquity, we decided to duplicate some logic from ubuntu-drivers to have the ability to do the above. See https://github.com/canonical/subiquity/pull/1700

Having a single implementation would be ideal so I would suggest adding a `ubuntu-drivers install-oem` or similar subcommand. This could also be implemented as a --oem-only flag that would do the opposite of --no-oem.