Allow enabling several log targets at once

Problem/Motivation

Now the module provides a radio selector of the target, where it will store the logs.

But sometimes developers want to put logs not only to one target, but to multiple ones. For example, to the file (as a long-term aggregated storage) and to the database (to have a convenient way to view logs directly in the Drupal admin panel).

Proposed resolution

To give this ability, it will be good to allow choosing multiple log targets in the settings, and submit the log enries to all the chosen targets at once.