Extract `changelog-check` to separate action

The `changelog-check` workflow helps us ensure that changelogs are updated alongside changes in polyrepos and monorepos.

Currently, when we make use of this workflow in other repos we need to pin to a specific commit ID. This is cumbersome because it means that if we want to make a change to the workflow we now need to go through each repo by hand and update the commit ID.

If we extracted this workflow to an action, we could start using version strings such as `v1`. As long as new changes were backward compatible they would automatically get propagated to all of the repos.

Inizia individuando il workflow changelog-check esistente e verificando come lo utilizzano gli altri repository. Estrailo in una GitHub Action versionata, aggiorna il modello di utilizzo per supportare i riferimenti in stile v1 e verifica che i controlli del changelog continuino a funzionare sia per i polyrepo sia per i monorepo.

Scritto dal modello di indicizzazione a partire dal testo della issue.