This introduces a settings updater that allows to specify a list of
settings. Whenever one of those settings changes, the whole block of
settings is passed to the consumer.
This also fixes an issue with affix settings, when used in combination
with group settings, which could result in no found settings when used
to get a setting for a namespace.
Lastly logging has been slightly changed, so that filtered settings now
only log the setting key.
Another bug has been fixed for the mock log appender, which did not
work, when checking for the exact message.
Closes#28047
a87714aafc