Pipelines-services - disconnected installation

[fgiloux]

It should be possible, preferably easy to install and configure Pipelines-services without internet connectivity:

• it should be possible to copy manifests and consume them offline (possibly in a private fork)
• it should be possible to copy container images and consume them offline (possibly from a private container registry)
• it should be possible by simple configuration to change the references to the above so that the installation and update process works without internet connection once the necessary content has been copied over.

[Roming22]

This issue is of particular importance for infrastructure that is running while being air-gapped (e.g. defense).