Lambda invoke builder `payload` docs are a bit off

### Describe the issue

The documentation for setting the payload are as follows:
```
The JSON that you want to provide to your Lambda function as input.

You can enter the JSON directly. For example, --payload '{ "key": "value" }'. You can also specify a file path. For example, --payload file://payload.json.
```

The second part of this looks like it's coming from CLI docs which aren't valid here.

### Links

- https://docs.rs/aws-sdk-lambda/0.25.1/aws_sdk_lambda/operation/invoke/struct.InvokeInput.html#method.payload
- https://docs.rs/aws-sdk-lambda/0.25.1/aws_sdk_lambda/operation/invoke/builders/struct.InvokeInputBuilder.html#method.payload
- https://docs.rs/aws-sdk-lambda/0.25.1/aws_sdk_lambda/operation/invoke/builders/struct.InvokeInputBuilder.html#method.set_payload
- https://docs.rs/aws-sdk-lambda/0.25.1/aws_sdk_lambda/operation/invoke/builders/struct.InvokeFluentBuilder.html#method.payload
- https://docs.rs/aws-sdk-lambda/0.25.1/aws_sdk_lambda/operation/invoke/builders/struct.InvokeFluentBuilder.html#method.set_payload

Start with the linked docs.rs pages for InvokeInput and its payload, set_payload, and fluent-builder methods. Compare the generated payload description with the issue's quoted text, remove or correct the CLI-specific guidance, and verify that the wording is consistent across all listed methods.

Written by the indexing model from the issue text.