Add an RBS signature for Aws::Query::Param

[kazuyainoue0124]

Here is my first PR to the aws-sdk-core repository.
I kindly ask for your understanding if there are any mistakes.

I have added an RBS type definition file, starting with just one file as a trial.

If this PR is successfully merged, I would like to continue contributing by adding more RBS type definitions in the future.

Thank you for taking the time to review this. I look forward to your feedback.

[mullermp]

Thanks for opening a pull request. We are happy to take RBS contributions. I'm wondering, why did you choose Aws::Query::Param specifically? I believe this a private API not intended to be used by customers. I think there is more value to RBS for public classes. That said, I'm not against taking this, but I'd like to see more than just this class added before we merge and bump the SDK version.

[kazuyainoue0124]

Thank you for your feedback, and I apologize for my misunderstanding.

I initially chose Aws::Query::Param because I assumed that any class without # @api private was part of the public API. I now realize this was incorrect. Moving forward, I’ll focus on contributing RBS for public classes.

Are there any specific indicators within the project, such as directory structures or naming conventions, to distinguish public APIs from internal ones? Or is comparing with the official documentation the primary way to make this determination?

Thank you for your patience and guidance.