Let target update mojo generate a report of changes

[laeubi]

Currently the target update just updates the target (what is useful of course), but it would be good to generate a markdown report like other mojos already do.

This should include:

1. New discovered versions (so one do not need to look at the diff)
2. A summary of the change in Imports and required capabilities compared to the last release to give an impression of possible additional requirements implied by the new version.