In T374431, we added a maintenance script that updates emergency defaults (to be checked into the repository). However, the path to them is currently hardcoded, even though it would make more sense if they were close to the schema files (as those two files are related to each other). The original idea was to allow extensions to customize that path via attributes. However, this is not readily possible, as ExtensionRegistry only returns attributes in their merged form (from _all_ extensions together), without including information about what extension defined what value. Hence, this is filled as a separate task, following up the work done in T374431.