feat: Refactor Google Drive and Google Photos authentication handling

- Separate built-in authentication options for source and destination in configuration forms.
- Update UI components to reflect changes in authentication handling for Google Drive and Google Photos.
- Implement path validation for local directories in the configuration forms, enhancing user experience.
- Revise README to clarify supported source and destination types, including updated terminology for Google Drive.
- Introduce new API endpoint for path validation, improving error handling and user feedback.

internal/db/migrations/migrations.go

@@ -8,16 +8,9 @@ import (
 // InitMigrations initializes the migrations
 func InitMigrations(db *gorm.DB) *gormigrate.Gormigrate {
 	migrations := []*gormigrate.Migration{
-		// ... existing migrations
-		AddDeleteAfterTransferColumn(),
-		AddCloudStorageFields(),
-		AddSkipProcessedFilesColumn(),
-		AddMaxConcurrentTransfersColumn(),
-		AddMultiConfigSupport(),
-		UpdateSkipProcessedFilesToNullable(),
-		AddWebhookSupport(),
-		AddGoogleDriveAuthenticated(),
-		AddGooglePhotosSupport(),
+		InitialSchema(),
+		UpdateBuiltinAuthFields(),
+		UpdateGDriveType(),
 	}
 
 	return gormigrate.New(db, gormigrate.DefaultOptions, migrations)