Rector the logger service

[zoglo]

Description

Found a usage within an old extension where the logger service was called like the first line in the diff below:

- $logger = System::getContainer()->get('logger');
+ $logger = System::getContainer()->get('monolog.logger.contao');

[aschempp]

Not sure that is correct? the monolog.logger.contao automatically adds a ContaoContext, but the regular service does not do that. And if I already wanted to log to the back end, I already had to add the ContaoContext?