fix: setup resource group for trigger and validate jobs

This MR fixes validation for MR created by a snapshot/release webhook from Jargon. trigger-payload creates/updates a MR and saves a webhook json from Jargon as a job artifact. validate-artefacts is triggered for a created/updated(?) MR with a source branch prefix specific to MRs created by trigger-payload. In order to make sure validate-artefacts downloads the right artefact from trigger-payload the are added to the same resource group. This prevents a new trigger-payload from starting while there is validate-artefacts in progress and vice versa.