Make config module/directory of repository-data configurable

In order to be able to keep using Essentials when upgrading to CMS 12 (while, conceptually and officially, this is still NOT SUPPORTED), since the old bootstrap/configuration module has been renamed to repository-data/config, and the latter is the default in Essentials 4.x, it should be possible to tell Essentials to consider this module located at the old path (bootstrap/configuration). The first part is already configurable by means of the tag

<repositoryDataModule>bootstrap</repositoryDataModule>

in the project-settings.xml file. This issue suggests to also make the second part (defaulting to "config") configurable.