TaskPrefix assignment does not follow 'system.reuseExistingDestination' flag.

Subject of the issue

There is a corner case where two datastreams could share a task prefix & consumer group despite expecting to output to two different topics.

Steps to reproduce

Tell us how to reproduce this issue.
Create datastream name "stream-1".
Create datastream name "dedupe-1". (dedupe-1 will now contain taskPrefix 'stream-1')
Delete "stream-1"
Recreate "stream-1" with metadata "system.reuseExistingDestination=false".

Expected behaviour

I would expect both streams to have different taskPrefixes (maybe through some uuid if system.reuseExistingDestination is present), different destination topics, and different consumer groups.

Actual behaviour

Both datastreams will still have taskPrefix "stream-1" despite the fact that with system.reuseExistingDestination=false both streams now have completely different destination topics.
The GroupIdConstructor logic will then assign the same consumer group to both streams and thus only one will actually get data.

Start with the TaskPrefix assignment and the GroupIdConstructor logic described in the issue, then reproduce the datastream creation, deletion, and recreation sequence. Done means streams using different destination topics receive distinct task prefixes and consumer groups when system.reuseExistingDestination=false.