fix: jargon artefacts validation

This MR fixes the dependency between a MR for a snapshot/release webhook create/update and artefacts validation - first we need to create or update a MR, and only after that run validation for the webhook payload. Also it sets a name for the pipeline triggerd by webhook, so it won't use a commit message from the latest commit on the mani branch which is very confusing. Another fix - trigger payload JSON data processing, client_payload was missing in jq commands to query data.