Refine custom embedder configuration support

- Update custom embedder configuration method to handle custom embedding functions
- Modify type hints for embedder configuration
- Remove unused model_name parameter in custom embedder configuration

docs/concepts/llms.mdx

@@ -463,32 +463,26 @@ Learn how to get the most out of your LLM configuration:
 
   <Accordion title="Google">
     ```python Code
-    # Option 1: Gemini accessed with an API key.
+    # Option 1. Gemini accessed with an API key.
     # https://ai.google.dev/gemini-api/docs/api-key
     GEMINI_API_KEY=<your-api-key>
 
-    # Option 2: Vertex AI IAM credentials for Gemini, Anthropic, and Model Garden.
+    # Option 2. Vertex AI IAM credentials for Gemini, Anthropic, and anything in the Model Garden.
     # https://cloud.google.com/vertex-ai/generative-ai/docs/overview
     ```
 
-    Get credentials:
-    ```python Code
-    import json
-
+    ## GET CREDENTIALS 
     file_path = 'path/to/vertex_ai_service_account.json'
 
     # Load the JSON file
     with open(file_path, 'r') as file:
         vertex_credentials = json.load(file)
 
-    # Convert the credentials to a JSON string
+    # Convert to JSON string
     vertex_credentials_json = json.dumps(vertex_credentials)
-    ```
 
     Example usage:
     ```python Code
-    from crewai import LLM
-
     llm = LLM(
         model="gemini/gemini-1.5-pro-latest",
         temperature=0.7,