Add Google Drive authorization processing and error handling templates

- Implemented `google_drive_callback.html` for processing Google Drive authorization, including UI for success and error states.
- Added JavaScript functionality for exchanging authorization codes, saving settings, and handling folder selection.
- Created `google_drive_callback_error.html` to display error messages during the authorization process.

app/utils/config_validator/__init__.py

@@ -0,0 +1,25 @@
+"""
+Configuration validation package for the application.
+"""
+
+from app.utils.config_validator.validators import (
+    validate_email_config,
+    validate_storage_configs,
+    check_all_configs
+)
+from app.utils.config_validator.masking import mask_sensitive_value
+from app.utils.config_validator.providers import get_provider_status
+from app.utils.config_validator.settings_display import (
+    get_settings_for_display,
+    dump_all_settings
+)
+
+__all__ = [
+    'validate_email_config',
+    'validate_storage_configs',
+    'mask_sensitive_value',
+    'get_provider_status',
+    'get_settings_for_display',
+    'dump_all_settings',
+    'check_all_configs'
+]