Export existing configuration into init_data.json

[Sjoerd82]

Would be nice if we could export existing settings into a init_data.json file.
This would make it easy to deploy new instances quickly from an existing instance.
Or reuse and deploy setting into new environments.

Related: #2461

[casbin-bot]

@tangyang9464 @JalinWang @imp2002

[hsluoyz]

@Sjoerd82 Data exported to file is supported, see docs: https://casdoor.org/docs/deployment/data-initialization/#export-config-data

[Sjoerd82]

Thanks, this helps a lot!