Flushing Cache when starting a content release could cause issues

[Sebobo]

Currently the Redis cache is flushed when a content release is started:

Flowpack.DecoupledContentStore/Classes/ContentReleaseManager.php

Line 62 in 195ef1f

$this->contentCache->flush();

This is not optimal as the content release might start later due to the pipeline configuration and parallel running releases influence each other.
Therefore only the cache entries should be flushed which are somehow related to the started release.