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/distributions/starter/run-with-postgres-store.yaml

@@ -47,7 +47,7 @@ providers:
   - provider_id: bedrock
     provider_type: remote::bedrock
     config:
-      api_key: ${env.AWS_BEDROCK_API_KEY:=}
+      api_key: ${env.AWS_BEARER_TOKEN_BEDROCK:=}
       region_name: ${env.AWS_DEFAULT_REGION:=us-east-2}
   - provider_id: ${env.NVIDIA_API_KEY:+nvidia}
     provider_type: remote::nvidia