text: Title: Add repeat() for iterable datasets
  Body: ### Feature request
  
  It would be useful to be able to straightforwardly repeat iterable datasets indefinitely, to provide complete control over starting and ending of iteration to the user.
  
  An IterableDataset.repeat(n) function could do this automatically
  
  ### Motivation
  
  This feature was discussed in this issue https://github.com/huggingface/datasets/issues/7147, and would resolve the need to use the hack of interleave datasets with probability 0 as a simple way to achieve this functionality.
  
  An additional benefit might be the simplification of the use of iterable datasets in a distributed setting:
  If the user can assume that datasets will repeat indefinitely, then issues around different numbers of samples appearing on different devices (e.g. https://github.com/huggingface/datasets/issues/6437, https://github.com/huggingface/datasets/issues/6594, https://github.com/huggingface/datasets/issues/6623, https://github.com/huggingface/datasets/issues/6719) can potentially be straightforwardly resolved by simply doing:
  
  ids.repeat(None).take(n_samples_per_epoch)
  
  
  ### Your contribution
  
  I'm not familiar enough with the codebase to assess how straightforward this would be to implement.
  
  If it might be very straightforward, I could possibly have a go.