chore(rename): move llama_stack.distribution to llama_stack.core (#2975)

We would like to rename the term `template` to `distribution`. To
prepare for that, this is a precursor.

cc @leseb

llama_stack/core/utils/dynamic.py

@@ -0,0 +1,13 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.
+
+import importlib
+
+
+def instantiate_class_type(fully_qualified_name):
+    module_name, class_name = fully_qualified_name.rsplit(".", 1)
+    module = importlib.import_module(module_name)
+    return getattr(module, class_name)