Add support for multiple deploy commands as well as nested choice options

Allowing both of these to usable at the same time seems like it could get dicey quick, and be misleading:

```yaml
production:
  deploy_cmd: 'check_if_deployable'
  deploy_cmds:
    - 'migrate all_the_things'
    - 'deploy all_the_things'
```

The order of the above would be run is `migrate all_the_things`, `deploy all_the_things`, `check_if_deployable`.