[Request]: `Image save` command: platform default to current

### Feature or enhancement request details

When saving an image pulled from remote sources, if the platform is nil, the save will failed with the notFound error:

For example, running
```
container image save alpine:latest --output /Users/itsuki/Desktop/untitled\ folder/image.tar
```
will give
```
Error: notFound: "Content with digest sha256:eafc1edb577d2e9b458664a15f23ea1c370214193226069eb22921169fc7e43f"
```

The digest here is not the digest for the image we are trying to save specifically, but the same for any (I think) remote images.

However, specifying the platform to be the current platform, in my case, --platform linux/arm64/v8, the save will success.

### Code of Conduct

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