Set variables for a yaml anchor reference

A more general use case for yaml anchors is to be able to pass variable values to the reference custom pipelines.  One way to do this would be to set up manual variables on the custom pipeline, and then set the values for those variables from the reference. There are likely other ways to approach this as well.

In some ways, this would also solve the use case in BCLOUD-19465 in a more general way.

Our current use case for this is to have a custom pipeline to run e2e tests against a deployment environment, but be able to parameterize that environment details (ie pass the url (or other parameters) to tell the custom pipeline what deployment environment to run the e2e tests against).

(I suppose this could be done with a custom pipe instead, but that seems like a lot of extra and external code, and it would be nice to have it all in the same repo).