Add DigitalOcean projects as option in the DigitalOcean machine driver
## Description
DigitalOcean offers projects to sort droplets in a better way.
This could be used for auto-created runners to get them out of the base folder.
## Proposal
Add an option like --digitalocean-project: to the DigitalOcean machine driver, so it can be used in config.toml
issue