details_url not outputting for production deploys

### The use case you're trying to solve

Production deploy doesn't set details_url output, but prints it in the action when run

### Change to the action that would solve that use case

ensure that for production deployment code the following is set as say line 101 in file https://github.com/FirebaseExtended/action-hosting-deploy/blob/0f248036885ae672f78587669fa2923f0ef6cac2/src/index.ts

```setOutput("details_url",url);```

### Other considerations

Although the url for production is known and static, for the purposes of using a github action, if the wiki says the output is available it should be, the Readme at https://github.com/FirebaseExtended/action-hosting-deploy#outputs should also be updated to reflect the following

urls
The url(s) deployed to (preview channels only)

expire_time
The time the deployed preview urls expire (preview channels only)

details_url
A single URL that was deployed to (production & preview)