feat: allow external trigger with edm4eic version

We have no good way of rolling out data models in testing pipelines or nightly builds.

This PR adds the ability to trigger the container build and downstream infrastructure with a data model in a git branch.

This should then allow the edm4eic pipelines to trigger this container build on a pull requests, to verify that the new data model is actually working before it is merged. It also rolls out the main branch of the data model in eic-shell (eic_xl:nightly) to allow users to develop against it when it is merged.

Tagged released eic-shell environments are still going to get the usual fixed version.