feat!: change bedrock bearer token env variable to match AWS docs & boto3 convention (#4152)

Rename `AWS_BEDROCK_API_KEY` to `AWS_BEARER_TOKEN_BEDROCK` to align with
the naming convention used in AWS Bedrock documentation and the AWS web
console UI. This reduces confusion when developers compare LLS docs with
AWS docs.

Closes #4147

src/llama_stack/providers/remote/inference/bedrock/bedrock.py

@@ -37,7 +37,7 @@ class BedrockInferenceAdapter(OpenAIMixin):
     """
 
     config: BedrockConfig
-    provider_data_api_key_field: str = "aws_bedrock_api_key"
+    provider_data_api_key_field: str = "aws_bearer_token_bedrock"
 
     def get_base_url(self) -> str:
         """Get base URL for OpenAI client."""
@@ -111,7 +111,7 @@ class BedrockInferenceAdapter(OpenAIMixin):
                 logger.error(f"AWS Bedrock authentication token expired: {error_msg}")
                 raise ValueError(
                     "AWS Bedrock authentication failed: Bearer token has expired. "
-                    "The AWS_BEDROCK_API_KEY environment variable contains an expired pre-signed URL. "
+                    "The AWS_BEARER_TOKEN_BEDROCK environment variable contains an expired pre-signed URL. "
                     "Please refresh your token by generating a new pre-signed URL with AWS credentials. "
                     "Refer to AWS Bedrock documentation for details on OpenAI-compatible endpoints."
                 ) from e