feat: add support for local ssh private keys

[NefixEstrada]

This should be the default behaviour, see the official Oracle plugin: https://github.com/hashicorp/packer-plugin-oracle/blob/main/builder/common/step_ssh_key_pair.go#L31

I give you my permission to modify and take the code as yours

[ShiChangkuo]

@NefixEstrada I don't understand the purpose of your design.
The user can directly use ssh_private_key_file to login the server, whose ssh key already contained in the source image.
So, I think we don't need to create a ssh keypair in HuaweiCloud to override the ssh key.