[dev] Extra logging fields

[PVince81]

Since 10.0.8 it is possible for developers to add additional JSON fields when creating log messages.

Example:

		$this->logger->info('Entity {entityName} has changed state to {newState}', [
			'app' => 'myapp',
			// these are used for text substitution in the above message
			'entityName' => 'X',
			'newState' => 'state2',
			// these will appear as additional JSON fields in the log entries
			'extraFields' => [
				'entityName' => 'X',
				'oldState' => 'state1',
				'newState' => 'state2',
				'entityOwner' => 'someuser',
			],
		]);

[mmattel]

master of 31121 owncloud/core#31135

[settermjd]

Backport to 10.1-3