Update railway add

[Milo123459]

This allows users to create services and databases in the linked project and environment, with similar options to the + Create menu found within the project canvas.

Changes and improvements are outlined below.

[coffee-cup]

Could we reuse the railway add command to cut down on the number of commands a user has to remember.

We could add options for empty service, docker image, and github repo. Right now railway create just makes an empty service and it would be nice if you could do something like railway add --name my-service --repo {pasted github link}. Or if you just do railway add you are prompted all the way through the process.

[brody192]

I agree having add as a single way of adding any kind of service(s) -- eventually bringing feature parity with the + Create modal in the project canvas.

For now, I think the format of railway add --service hello-world would fit best with how railway add currently works.

railway add --service -> Creates an empty service with a random name.
railway add --service hello-world -> Creates an empty service with the specified name.

And you can provide either a --repo or an --image flag to set the source, omitting them creates an empty service.

railway add --service hello-world --repo "brody192/hello-world" -> Creates a service that deploys from the given repo with the specified name.
railway add --service hello-world --image ubuntu -> Creates a service that deploys from the given image with the specified name.

Additionally, you would also be able to pass --variables to the --service flag in k=v format.

railway add --service hello-world --variables "VARIABLE=VALUE" -> Creates an empty service with the specified name and the specified variable(s).

For the interactive flow when running just railway add it should prompt similarly to how the + Create button does.

GitHub Repo
Database
Docker Image
Empty Service

With all the same flag-based functionality but fully interactive.

We can worry about deploying templates via railway add at a later time.

Why though?

This brings us a few steps closer to parity with the dashboard, meaning if you love the terminal you now can stay in it a little longer!

But for a real world scenario, this allows users to add variables to a service prior to deployment, this means less unnecessary redeployments due to having to add variables via the dashboard and then redeploy.