Make grub2-xen-pvh a dependency of dom0 config rpm

[rocodes]

Status

Work in progress (Code-complete but corresponding changes elsewhere are needed, see below)

Description of Changes

Fixes #1063.

Changes proposed in this pull request:
Make grub2-xen-pvh a dependency of the dom0 config rpm.

This requires the rpm to be installed with network access (i.e. qubes-dom0-update instead of via dnf), so it's blocked on the existence of the securedrop-workstation-keyring package, and of the install mechinism of the dom0 config rpm changing to sudo qubes-dom0-update securedrop-workstation-dom0-config.

(Will require workstation CI changes, tbd)

Testing

If you made non-trivial code changes, include a test plan and validated it for this PR.

Deployment

Any special considerations for deployment? Consider both:

1. Upgrading existing pilot instances
2. New installs

Checklist

If you have made changes to the provisioning logic

• All tests (make test) pass in dom0

If you have added or removed files

• I have updated MANIFEST.in and rpm-build/SPECS/securedrop-workstation-dom0-config.spec

If documentation is required

• I have opened a PR in the docs repo for these changes, or will do so later
• I would appreciate help with the documentation