Update container for new eic_container structure

The raison d'être for the juggler container is to provide a quicker workflow that integrates recent changes to the reconstruction while side-stepping the need to rebuild the full eic_container chain (which is much slower). Functionally it is identical to the nightly, except that it is available on commit to the juggler master. For this reason, we do not need fancy versioned releases, and we should push this container to the eic_container registry instead of the juggler registry, and we should just tag it as nightly (as it is identical!).

• Use jug_dev:testing as base container
• Use eic_container tooling for Gitlab CI
• Use jug_xl Dockerfile to build container to ensure have a proper nightly build.
• Remove versioned juggler container builds - jug_xl should be the one-stop-shop for our container.
• Ensure MR-related workflows still function