S3: GetObjectRequest toFile option to override file

Migrating from SDK V1 to V2 we hit an issue where do something like this (pseudo-code):
```
Path temp = Files.createTempFile(...);
s3.getObject(bucket, key, temp);
// use temp file
```
This allows us to download a temp file, validate it and if we are happy flip it to the actual path overriding the existing previous file.

This works on V1 because: because it just opens an outputstream which by default overwrites ([here](https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-s3/src/main/java/com/amazonaws/services/s3/internal/ServiceUtils.java#L304))
but doesn't work on V2 because we are not passing any options to `Files.copy` ([here](https://github.com/aws/aws-sdk-java-v2/blob/master/core/sdk-core/src/main/java/software/amazon/awssdk/core/sync/ResponseTransformer.java#L106))

## Describe the Feature

Allow the use of S3 client to download an object to an existing file by overwriting it

## Is your Feature Request related to a problem?

See general summary

## Proposed Solution

* Suggestion 1 (preferred): adding an overload with a boolean `overwrite` for this `toFile` method [here](https://github.com/aws/aws-sdk-java-v2/blob/master/core/sdk-core/src/main/java/software/amazon/awssdk/core/sync/ResponseTransformer.java#L102) that can be passed to the `Files.copy` call as `StandardCopyOption.REPLACE_EXISTING` (only option allowed when using `Files.copy` with an input stream)
* Suggestion 2 (less preferred because it's ugly but works): Add another method in `ResponseTransformer`, e.g. `ResponseTransformer.toFileOverwrite`
* Suggestion 3 (not preferred because it's a breaking change): Change the default behaviour and hardcode `StandardCopyOption.REPLACE_EXISTING`

## Describe alternatives you've considered

See suggestion 2/3 in proposed solution

## Additional Context

- [x] I may be able to implement this feature request

## Your Environment

* AWS Java SDK version used: N/A
* JDK version used: N/A
* Operating System and version: N/A