Install securedrop-workstation-keyring boostrap RPM in CI and use it to download dom0 config

[rocodes]

Refs freedomofpress/securedrop-workstation#1209 : When we move to a bootstrap RPM, install it and then switch the dom0 config rpm installation mechanism to sudo qubes-dom0-update securedrop-workstation-dom0-config.

Needs discussion and subcomponents before ready to configure.

Additionally, per freedomofpress/securedrop-workstation#1210 , we may want a mechanism that ensures that for non-prod repos (including CI), there is an additional guardrail against provisioning against dev, staging or qa yum repos, such as the requirement of a local-only devtools package. If so, that will need to be installed in CI as well.

(More tk)