text: Title: support for debugging R scripts
  Body: Currently, the `Task.debug()` method only works on Python. If someone tries to debug an R script, this happens:
  
  ```py
  ---------------------------------------------------------------------------
  NotImplementedError                       Traceback (most recent call last)
  <ipython-input-5-828509ada065> in <cell line: 1>()
  ----> 1 dag['model-run-adultsVsChildren-child'].debug()
  
  ~/opt/anaconda3/envs/wordsense_pipeline/lib/python3.8/site-packages/ploomber/tasks/notebook.py in debug(self, kind)
      382         """
      383         if self.source.language != 'python':
  --> 384             raise NotImplementedError(
      385                 'debug is not implemented for "{}" '
      386                 'notebooks, only python is supported'.format(
  
  NotImplementedError: debug is not implemented for "r" notebooks, only python is supported
  ```
  
  We should implement support for debugging R scripts. The implementation isn't that difficult and will be very similar to what we already have for [Python scripts](https://github.com/ploomber/ploomber/blob/2d92ebcea2055da169eadd22dd5afa4d953d878e/src/ploomber/tasks/notebook.py#L373).
  
  ## Implementation observations
  
  ### providing context to the user
  
  To facilitate learning how to use the debugger we should add a new FAQ that explains how to debug R scripts and add a link to it in the error message. something like:
  
  ```python
  >>> task.debug()
  ```
  
  ```
  You started a debugging session, to learn more: https://ploomber/s/r-debug
  ```
  
  we need to add a new file here:
  
  https://github.com/ploomber/ploomber/tree/master/doc/user-guide/faq
  
  and then list it here:
  
  https://github.com/ploomber/ploomber/blob/master/doc/user-guide/faq_index.rst
  
  once that's done, ping @edublancas so he can create the short URL (`https://ploomber/s/r-debug`)
  
  ### Default values
  
  We need to change the default values of the `.debug()` function, it's currently set to `kind='ipdb'` - but that's a Python-specific value. I think we should change it to `kind=None`.
  
  Then figure out the actual default depending on Python (ipdb), or R (None)
  
  ### debugging session
  
  the current implementation supports two debugging modes in Python. Starting a debugging session that allows you to move line by line in a script (using either ipdb or pdb) and a post-mortem session (which runs the scripts and then it starts the debugger once it throws an error).
  
  based on [this](https://adv-r.hadley.nz/debugging.html#browser-commands), it looks like `browser()` is the equivalent in R to pdb in Python, essentially, we'd need to add a `browser()` line at the beginning of the script and then start a subprocess so start the debugging session
  
  ### post-mortem debugging
  
  the second debugging option is post-mortem, which runs the script and starts the debugging session once it fails. In R, it looks like adding [options(error = recover)](https://rdrr.io/r/base/options.html) at the top of the script will work.
  
  ## options matrix
  
  These are the possible values for the `kind` argument in the `debug()` method depending on the language:
  
  *Python*
  ipdb, pdb and pm (remain without changes)
  
  *R*
  None: starts a debugging session (aka it uses `browser()`)
  pm: starts a post-mortem session (aka it uses  `options(error = recover)`)
  
  If we're dealing with an R script and we get a value that is not None or pm we should throw an error. Same with Python (we should only accept ipdb, pdb, pm and None). In the case of None, we replace it internally by ipdb.
  
  
  
  
  