feat: bundle app config

[doitian]

Proposal: [PREVIEW]

• Add ckb_resource::ResourceLocator to load config files, which fallbacks to the bundled files.
• Add a new subcommand ckb init to dump the bundled config files.
• The bundled config files support template to set the different options for different specs in the same file.
• Add many checks before starting the app.
• Refactor the code organization in src.
• Options logger.file, db.path and network.path are set automatically from the data dir.

Breaking Changes:

• Remove command line argument -c, and add command line argument -C.
• No longer search the config file nodes/default.toml.
• Remove logger.file, db.path and network.path from config file. Add config option logger.copy_to_stdout.

Future Enhancements:

• Better exit message.
• Verify genesis hash when starting the app.
• Verify database version when starting the app.

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TODO

• Add tests to load bundled config files.
• Add tests to load the config files generated by ckb init.
• ckb init should quit if any file already exists unless --force is specified.
• ckb init should write file to temp file first, and move to the target location to avoid generating partial file because of interrupts.

[doitian]

Rebased onto rc/v0.9.0

#425