refactor(cli): move out to its own packages (#619)

Signed-off-by: Aaron <29749331+aarnphm@users.noreply.github.com>

openllm-python/src/openllm_cli/extension/__init__.py

@@ -0,0 +1,16 @@
+"""OpenLLM CLI Extension.
+
+The following directory contains all possible extensions for OpenLLM CLI
+For adding new extension, just simply name that ext to `<name_ext>.py` and define
+a ``click.command()`` with the following format:
+
+```python
+import click
+
+@click.command(<name_ext>)
+...
+def cli(...): # <- this is important here, it should always name CLI in order for the extension resolver to know how to import this extensions.
+```
+
+NOTE: Make sure to keep this file blank such that it won't mess with the import order.
+"""