Add a separate (sshfs-) fetch job to pull in an existing ostree remote
The build job currently has an optional dependency on SSHFS credentials to pull-in a remote before starting the build so it may build a correct history. To simplify the build job this can be done in a separate job before the build at the beginning of the pipeline.
This job could also pull other resources required for the build.
The transport can either be done through cache or artifacts as discussed in #55