config: let server to return dynamic visitor more earlier - #47521

Commit Message: config: let server to return dynamic visitor more earlier
Additional Description:

1. Now, the bootstrap_config_loaded_ could be a strict flag between static configuration loading and dynamic configuration loading (xds, include the file based xds). So, the server's visitor should could be used as default always.
2. Server will return dynamic visitor more earlier, so, it won't break existing users which means looser restrictions.

Risk Level:
Testing:
Docs Changes:
Release Notes:
Platform Specific Features:
[Optional Runtime guard:]
[Optional Fixes #Issue]
[Optional Fixes commit #PR or SHA]
[Optional Deprecated:]
[Optional API Considerations:]