Improve the procedure to convert Forte pipeline to YAML

[zhanyuanucb]

Is your feature request related to a problem? Please describe.
Collaborating with some submission tools to submit a Forte pipeline often requires saving the pipeline config. It will be convenient to have a method to tell Forte pipeline from which dir the submission tool will pick up the serialized pipeline.

Describe the solution you'd like
Add an export method to Pipeline. This method takes in a commit_name and checks if a hidden environment variable FORTE_EXPORT_PATH is assigned. If that is the case, then this method will name the pipeline config <commit_name>.yml and dump it to that dir.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
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