Allow configuring a general exclusion list for backup-globals

[ErikBrendel]

It is possible to exclude some global variables for the global-backup-system via an annotation on class or method level.

Example:

#[\PHPUnit\Framework\Attributes\ExcludeGlobalVariableFromBackup('wpdb')]
class MyTest { /* ... */ }

I would really like to be able to define such an exclusion globally, i.e. for the whole test run and all test cases. I would expect there to be a CLI argument and/or an XML configuration option, simiar to the existing flag option for backupGlobals.