migrate the external pipeline according to the details noted in the parent task (OCMUI-2632):
build-deploy jobs for long-lived branches (push to quay).

in addition:

• we're probably gonna need to switch off the GL<––>GH sync job, to avoid built container-images from the two repo's overwriting each other in quay.io
• we might want to take stable out of the equation, and only utilize the master build job for now, to make the transition easier
• we can delete the old webhook from GL, as its name will have been changed