WIP: Resolve "Deploy source code to public repository"

What does this MR do?

Deploy the DORiE source code to the repository at https://gitlab.dune-project.org/lukas.riedel/dorie

• Add secret SSH key as SSH_PRIVATE_KEY secret variable
• Add host key to secret variable SSH_KNOWN_HOSTS
• Add public key as 'Deploy Key' to remote repository
• Create 'deploy' stage and appropriate job
  • Declare environment for this job

Is there something that needs to be double checked?

Can this MR be accepted?

• Pipeline passing

Related issues

Closes #51 (closed)