CLI support for encoding/importing from JSON

### Things to check first

- [X] I have searched the existing issues and didn't find my feature already requested there

### Feature description

Currently the CLI tool only supports converting CBOR data to representation that allows printing as JSON. The reverse serialization / importing is also a common task.

Happy to contribute as well.

### Use case

It's convenient for manual testing with human readable JSON files/payload. Supported in this Rust project as well https://github.com/TakenPilot/cbor-cli.

Examples:

`cbor2 -o test.cbor test.json --format=json`