### What
- Added `AuthConfig` v2 config example in
`static/auth/auth_config_v2.json`
- Moved exisiting `auth_config.json` to `static/auth/`
- Removed unused `pre_plugins.json`
If one wants to start the engine with a v2 of AuthConfig,
`static/auth/auth_config_v2.json` can be used.
V3_GIT_ORIGIN_REV_ID: 471f8ae43ab02c2182457804a24b8445bb41f06c
