Change post training run.yaml inference config (#710)

## Context
Colab notebook provides some limited free T4 GPU. 

Making post training template e2e works with colab notebook T4 is
critical for early adoption of the stack post training apis. However, we
found that the existing LlamaModelParallelGenerator
(https://github.com/meta-llama/llama-stack/blob/main/llama_stack/providers/inline/inference/meta_reference/inference.py#L82)
in meta-reference inference implementation isn't compatible with T4
machine.

In this PR, We change to disable create_distributed_process_group for
inference api in post training run.yaml config and setup up the
distributed env variables in notebook
<img width="493" alt="Screenshot 2025-01-02 at 3 48 08 PM"
src="https://github.com/user-attachments/assets/dd159f70-4cff-475c-b459-1fc6e2c720ba"
/>

to make meta reference inference compatible with the free T4 machine

 ## test
Test with the WIP post training showcase colab notebook
https://colab.research.google.com/drive/1K4Q2wZq232_Bpy2ud4zL9aRxvCWAwyQs?usp=sharing

llama_stack/templates/experimental-post-training/run.yaml

@@ -19,6 +19,7 @@ providers:
     config:
       max_seq_len: 4096
       checkpoint_dir: null
+      create_distributed_process_group: False
   eval:
   - provider_id: meta-reference
     provider_type: inline::meta-reference