docstr: save pipeline to file, contains feature transformer, model, trial config.
  :param ppl_file:
  :return:
docstr_tok: ["save","pipeline","to","file",",","contains","feature","transformer",",","model",",","trial","config",".",":","param","ppl_file",":",":","return",":"]
code: def save(self, ppl_file=None):
      """
      save pipeline to file, contains feature transformer, model, trial config.
      :param ppl_file:
      :return:
      """
      ppl_file = ppl_file or os.path.join(
          DEFAULT_PPL_DIR, "{}_{}.ppl".format(self.name, self.time)
      )
      self.model.save(ppl_file)
      return ppl_file
  
file_path: BigDL/python/chronos/src/bigdl/chronos/autots/deprecated/pipeline/time_sequence.py
imports: import os
  import time
  from bigdl.chronos.autots.deprecated.feature.utils import save_config
  from bigdl.chronos.autots.deprecated.pipeline.base import Pipeline
  from bigdl.chronos.autots.deprecated.model.time_sequence import TimeSequenceModel
  from bigdl.chronos.autots.deprecated.pipeline.parameters import DEFAULT_CONFIG_DIR, DEFAULT_PPL_DIR
  from bigdl.chronos.utils import deprecated
label_desc: Use image node_id 8 for calling the TimeSequencePipeline obj's underlying member method code with example usage: obj.save(ppl_file) and returns: ppl_file