Why not have a single deploy action?

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

I want to deploy everything, including functions, in a single action.

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

This action is very useful, as it can create a preview for each PR individually. I don't think this functionality is working yet for Experimental Frameworks: Svelte, as I can see it in the live channel, but not in a preview one. That's beside the point, though.

My point is: why should this action just deploy to hosting and leave aside "database", "firestore", "functions", and so on, to be deployed in a separate step?