Self-documenting settings template

[Vassiliy-Kudryashov]

Description

At the moment we don't provide settings.properties file for users. Moreover there is no documentation for this file, and we don't create it by default.

Expected behavior

As soon as the only source of knowledge is our sourcecode (namely UtSettings.kt) we should generate settings.properties as resource file inside plugin archive and provide settings template in user's {home}/.utbot/settings.properties with all default values and documentation from corresponding sourcecode comments.

The generation should be part of "IntelliJ" Gradle task

Note: we shouldn't re-write settings.properties if the file is presented with some custom (not default) user-defined values.