extension-release: search for other files if expected name not found

extension-release: search for other files if expected name not found

In some cases image names are unpredictable - some orchestrators/deployment
tools like to mangle names to suit their internal formats. In these cases,
the requirement that the extension-release file matches exactly the image
name where it's contained cannot work.

Allow falling back to loading the first regular file which name starts with
'extension-release' located in /usr/lib/extension-release.d/ and tagged with
a user.extension-release.strict extended attribute with a true value, if the
one with the expected name cannot be found.