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

tests/unit/cli/test_stack_config.py

@@ -9,7 +9,7 @@ from datetime import datetime
 import pytest
 import yaml
 
-from llama_stack.distribution.configure import (
+from llama_stack.core.configure import (
     LLAMA_STACK_RUN_CONFIG_VERSION,
     parse_and_maybe_upgrade_config,
 )