Support CLI to access core entities in terminal #219

We should support the gitploy CLI for users who love using the terminal. If users want to interact with Gitploy in CI or a script, CLI support would be best.

Todo (v0.6)

• Design the client package API #313
• Initialize the 'cli' package #321
• Add repo subcommand to interact with Repo entities #319
• Provide the subcommand to access Deployment by CLI command #323
• Provide the config subcommand to read configurations #327
• Provide the deployment-status subcommand to access the statuses #332