Fix: If dangling_timeout was set to 0 and auto_import_dangled

was set to yes, dangling indices were deleted by mistake,
because a RemoveDanglingIndices runnable was added
to every dangling indices, without considering the auto_import_dangled
setting.
@bogensberger My thought here was that although the timeout should have no effect given `auto_import_dangled` is set to true, it would be good if there was a test that ensures that this is the case so that the code is protected against regressions. By using a randomised value here we can test with various timeouts and ensure that we don't accidentally change the functionality to rely on the `dangling_timeout` being set to `0`in the future.