[feature]: Add an option to pass the config file

[yu-iskw]

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Overview

The bigfun command doesn't offer any option to specify the path to a config file. It can read only the default path. If we add an option to pass it, we can more easily switch the deployment destination. For instance, we have the environments for the development and the production. We want to share the deployed functions in both by switching the config file.

bigfun deploy --config path/to/config.yaml