chore: rename templates to distributions (#3035)

As the title says. Distributions is in, Templates is out.

`llama stack build --template` --> `llama stack build --distro`. For
backward compatibility, the previous option is kept but results in a
warning.

Updated `server.py` to remove the "config_or_template" backward
compatibility since it has been a couple releases since that change.

llama_stack/providers/remote/datasetio/nvidia/README.md

@@ -20,7 +20,7 @@ This provider enables dataset management using NVIDIA's NeMo Customizer service.
 Build the NVIDIA environment:
 
 ```bash
-llama stack build --template nvidia --image-type venv
+llama stack build --distro nvidia --image-type venv
 ```
 
 ### Basic Usage using the LlamaStack Python Client

llama_stack/providers/remote/inference/nvidia/NVIDIA.md

@@ -18,7 +18,7 @@ This provider enables running inference using NVIDIA NIM.
 Build the NVIDIA environment:
 
 ```bash
-llama stack build --template nvidia --image-type venv
+llama stack build --distro nvidia --image-type venv
 ```
 
 ### Basic Usage using the LlamaStack Python Client

llama_stack/providers/remote/post_training/nvidia/README.md

@@ -22,7 +22,7 @@ This provider enables fine-tuning of LLMs using NVIDIA's NeMo Customizer service
 Build the NVIDIA environment:
 
 ```bash
-llama stack build --template nvidia --image-type venv
+llama stack build --distro nvidia --image-type venv
 ```
 
 ### Basic Usage using the LlamaStack Python Client

llama_stack/providers/remote/safety/nvidia/README.md

@@ -19,7 +19,7 @@ This provider enables safety checks and guardrails for LLM interactions using NV
 Build the NVIDIA environment:
 
 ```bash
-llama stack build --template nvidia --image-type venv
+llama stack build --distro nvidia --image-type venv
 ```
 
 ### Basic Usage using the LlamaStack Python Client