[feature request] Add support for deploy key

It would be nice to be able to use deploy keys to commit to the repo instead of api tokens. This would allow using this tool to be more self-service at some corporations that may have different workflows for API Token generation.

Use case: A team of developers would like to use release in their pipeline. API tokens require multiple tickets to IT in order to get setup.

Benefit: The repo maintainers would be able to generate and apply deploy tokens that could then be used in the pipeline without needing to wait for IT.

I would like to propose a flag that would allow for using ssh instead of https for pushing commits. Something like --deploy-key $DEPLOY_KEY||/.ssh/my_deploy_key

Secret key can either get into pipeline directly through $DEPLOY_KEY env variable, or by

- eval $(ssh-agent -s)
- ssh-add <(echo "$SSH_PRIVATE_KEY")