Add new command: configuration:showbypath

Show configuration values from $GLOBALS['TYPO3_CONF_VARS'].
Supports both full paths and parts of a path.

Examples:
./typo3cms configuration:showbypath SYS/caching/cacheConfigurations/cache_core
./typo3cms configuration:showbypath SYS/caching/cacheConfigurations/cache_core/frontend