Inconsistent Data API "Add custom queries and mutations" code samples

**Describe the content issue**:
A clear and concise description of what the content issue is. Is there content missing or is there incorrect content?

1. Auth in [Step 1](https://docs.amplify.aws/gen2/build-a-backend/data/custom-business-logic/#step-1---define-a-custom-query-or-mutation) does not match auth in [Step 2](https://docs.amplify.aws/gen2/build-a-backend/data/custom-business-logic/#step-2---configure-custom-business-logic-handler-code) (Step 1 is `private`, Step2 is `public`). Since we are walking customers through building these resources step-by-step, these auth rules should match.
2. "Function" code sample for `amplify/data/echo-handler/handler.ts` under [Step 2](https://docs.amplify.aws/gen2/build-a-backend/data/custom-business-logic/#step-2---configure-custom-business-logic-handler-code) includes unused `context` parameter.

**URL page where content issue is**:
https://docs.amplify.aws/gen2/build-a-backend/data/custom-business-logic/