User-provided image tag for TopCP transformer

[kyungeonchoi]

Story

The container image for ServiceX TopCP transformer is pinned to a specific version of TopCPToolkit framework built and published from our own repository (science-images). It's very common that users or physics analysis groups keep update TopCPToolkit to add more features or information. Currently it's practically not possible to run different version of TopCPToolkit framework in ServiceX.

Plan

TopCPToolkit image

@kyungeonchoi is maintaining the GitLab repository of TopCPToolkit framework for BLS group. Add GitLab action (CI/CD pipeline) to build a container whenever new release (together with a new tag) is published. Also push to GitLab container registry to be able to pulled from ServiceX backend.

ServiceX frontend

ServiceX frontend library needs to be updated to be able to pass image tag for TopCP transformer. Below is the possible example:

Sample:
  - Name: "ttbar"
    Dataset: dataset.Rucio("data18_13TeV:data18_13TeV.example")
    Query: query.TopCP(reco="reco.yaml", image_tag="v2.20.0_v0.2")

ServiceX backend

ServiceX backend needs to be able to pull the user-provided image tag for TopCP transformer. I think it should be restricted to the specific GitLab repository where we know who published the image.