Creates and Adds a file handler (`logging.FileHandler` instance) to the specified logger. 

  Args:
      logger: The `logging.Logger` instance to add the new file handler to.
      level: `str`. The logging level for which the handler accepts messages, i.e. `logging.INFO`.
      tags: `list` of tags to append to the log file name. Each tag will be '_' delimited. Each tag
           will be added in the same order as provided.

def add_file_handler(logger,level,tags):
  """Creates and Adds a file handler (`logging.FileHandler` instance) to the specified logger. 

  Args:
      logger: The `logging.Logger` instance to add the new file handler to.
      level: `str`. The logging level for which the handler accepts messages, i.e. `logging.INFO`.
      tags: `list` of tags to append to the log file name. Each tag will be '_' delimited. Each tag
           will be added in the same order as provided.
  """
  f_formatter = logging.Formatter('%(asctime)s:%(name)s:\t%(message)s')
  filename = get_logfile_name(tags)
  handler = logging.FileHandler(filename=filename,mode="a")
  handler.setLevel(level)
  handler.setFormatter(f_formatter)
  logger.addHandler(handler)