In order to work around the lack of a "origin filter" in DW, let's add support for ExternelCI via shadow checkouts and builds, like KQE is doing today, by taking their IDs and replacing the "redhat" origin with each of the ExternalCI names, taken from the ExternelCI labels in MR (today, only LNST).

AC:

• [ ] Take ExternalCI labels from the MR in pipeline-definition
• [ ] Create Checkouts and Builds for each of them (possibly in the `merge` stage.

Jira: CKI-6464