docs: Update OpenAI-compatible provider config format (#37517)

The example was still showing how we used to setup openai compatible
providers, but that format should only be used for changing the url for
your actual OpenAI provider.

If you are doing a compatible provider, it should be using the new
format.

Closes #37093

Release Notes:

- N/A

docs/src/ai/llm-providers.md

@@ -435,21 +435,24 @@ To do it via your `settings.json`, add the following snippet under `language_mod
 ```json
 {
   "language_models": {
-    "openai": {
-      "api_url": "https://api.together.xyz/v1", // Using Together AI as an example
-      "available_models": [
-        {
-          "name": "mistralai/Mixtral-8x7B-Instruct-v0.1",
-          "display_name": "Together Mixtral 8x7B",
-          "max_tokens": 32768,
-          "capabilities": {
-            "tools": true,
-            "images": false,
-            "parallel_tool_calls": false,
-            "prompt_cache_key": false
+    "openai_compatible": {
+      // Using Together AI as an example
+      "Together AI": {
+        "api_url": "https://api.together.xyz/v1",
+        "available_models": [
+          {
+            "name": "mistralai/Mixtral-8x7B-Instruct-v0.1",
+            "display_name": "Together Mixtral 8x7B",
+            "max_tokens": 32768,
+            "capabilities": {
+              "tools": true,
+              "images": false,
+              "parallel_tool_calls": false,
+              "prompt_cache_key": false
+            }
           }
-        }
-      ]
+        ]
+      }
     }
   }
 }
@@ -463,7 +466,7 @@ By default, OpenAI-compatible models inherit the following capabilities:
 - `prompt_cache_key`: false (does not support `prompt_cache_key` parameter)
 
 Note that LLM API keys aren't stored in your settings file.
-So, ensure you have it set in your environment variables (`OPENAI_API_KEY=<your api key>`) so your settings can pick it up.
+So, ensure you have it set in your environment variables (`<PROVIDER_NAME>_API_KEY=<your api key>`) so your settings can pick it up. In the example above, it would be `TOGETHER_AI_API_KEY=<your api key>`.
 
 ### OpenRouter {#openrouter}