Change `this.input` to `args.input ` in `DocumentMarshall` middleware

[zshzbh]

Describe the feature

Source code
In order to mutate the input of DynamoDBDocumentClient operations, we need to add addRelativeTo with { relation: "after", toMiddleware: "DocumentMarshall" } .

This is because we assign this.input to args.input in DocumentMarshall middleware - args.input = marshallInput(this.input, this.inputKeyNodes, marshallOptions);

Change this.input to args.input in DocumentMarshall middleware, so that we can use stack.add with step:initial`` to mutate the input.

This is related to this issue - #6743

Use Case

we can use stack.add with step:"initial" to mutate the input.

Proposed Solution

Change this.input to args.input in DocumentMarshall middleware

Change
args.input = marshallInput(this.input, this.inputKeyNodes, marshallOptions);
to
args.input = marshallInput(args.input, this.inputKeyNodes, marshallOptions);

Other Information

No response

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

SDK version used

latest

Environment details (OS name and version, etc.)

OS

[alfaproject]

I would say this is a bug fix and not a feature request (;