Get key by name

### Checklist

- [X] My issue is specific & actionable.
- [X] I am not suggesting a protocol enhancement.
- [X] I have searched on the [issue tracker](https://github.com/ipfs/kubo/issues?q=is%3Aissue) for my issue.

### Description

Forum discussion: https://discuss.ipfs.tech/t/get-key-by-name/17901

Kubo lets the user create keys by name `ipfs key gen ` but currently the only way to get a public key given its name is to parse the list of keys output by `ipfs key list -l`.

The idea of the feature would be to allow the user to retrieve the public key by name with something like `ipfs key get --name `.