Add outputs to action

[1000hz]

As requested in #210, it would be useful for this action to provide some outputs to allow users to consume the results of the action run in subsequent workflow steps.

For the MVP, we could start with providing a command-output that makes the stdout from executing command available. We could also possibly try to detect if a workers or pages deployment was made and provide a deployment-url we infer from the output.

[admah]

Would solving this issue help with this?

[1000hz]

Not quite, though that could still be useful to people. What this issue refers to is there's currently no way to consume output from the action in other workflow steps because we're not setting outputs via the APIs GitHub Actions provides for this.