Logging: restrict files loaded as logging configuration based on their suffix

Make sure that files such as logging.yml.rpmnew or logging.yml.bak are not loaded as logging configuration.

Only files that start with the "logging." prefix and end with ".yaml", ".yml", ".json" and ".properties" suffix get loaded.

Closes #7457
[TEST] move LoggingConfigurationTests to common.logging.log4j

Make also LogConfigurator#ALLOWED_SUFFIXES package private so that it can be used in LoggingConfigurationTests, now that it's in the same package as the class that it tests.
Add few randomized aspects to LoggingConfigurationTests.
[DOCS] document that we support loading multiple logging conf files