The head content in the workspace live is not always the same :

1. On content validation (if the content is not already published)
2. On content validation (if the content is already published)
3. On live rebuild

On first case and last case, we get the last validated content into the version history and treat some metadatas manually (SynchronizeContentValidationObserver catch treatment and SitePopulator).

It's a different behaviour for the second case because it takes the head version in the default workspace to get metadatas (SynchronizeContentValidationObserver try treatment).
Because of this, we sometimes copy metadata which are not set by case 1 and 3, like ametys-internal:consistency node.

We should factorize the SynchronizeContentValidationObserver code and add an helper to avoid code duplication.