Migrate sourcesecret package to runtime/secrets APIs

The sourcesecret package now uses pkg/runtime/secrets factory
functions instead of the previous monolithic approach. This
provides standardized secret generation with consistent
validation and error handling across all authentication types.

Signed-off-by: cappyzawa <cappyzawa@gmail.com>

pkg/bootstrap/bootstrap_plain_git.go

@@ -236,7 +236,7 @@ func (b *PlainGitBootstrapper) ReconcileSourceSecret(ctx context.Context, option
 
 	// Generate source secret
 	b.logger.Actionf("generating source secret")
-	manifest, err := sourcesecret.Generate(options)
+	manifest, err := sourcesecret.GenerateGit(options)
 	if err != nil {
 		return err
 	}