AT:

• the tests are running green again
• the reimport preperation also works for a large dataset
• the new version of the module is added to the upgrade docs

Context:
Before/after an upgrade of Optimize might want to reimport the engine data, otherwise they can't use all the features of the new Optimize version. For a detailed description see the dedicated documenation.

Hint:
Probably we should delete the process instance/process-definition/xml/import-index Elasticsearch indexes and then create a new mapping for them. However, then we need to make sure that we update this module for each release, since the Elasticsearch data structure might have changed.