Production base template for beta release

[emkll]

Closes freedomofpress/securedrop-workstation#424

Promoting dev artifacts introduced in freedomofpress/securedrop-yum-test#7, with build logs available in freedomofpress/build-logs@cfe5e23

In order to fully test the provisioning logic for production scenarios, we will need:

• securedrop-workstation-dom0-config RPM package in this repository
• All subproject packages on apt.freedom.press (tracked in another repo:
  • securedrop-client
  • securedrop-log
  • securedrop-proxy
  • securedrop-export

Test plan

• Ensure unsigned template in 87059eb is identical to the one in freedomofpress/securedrop-yum-test@2599022
• sha256sum of template with signature remove is same as the one in the dev commit message freedomofpress/securedrop-yum-test@f1b9021
• CI logic is sound, and key is the securedrop release key
• CI is passing

[conorsch]

Looks great. Checked out locally in order to compare checksums on dev rpm.