Use composite actions to setup scarb in this action

We can convert this action to be a composite action: https://docs.github.com/en/actions/creating-actions/creating-a-composite-action and setup scarb by reusing the https://github.com/software-mansion/setup-scarb action.

Details of this should be discussed but we need to remember to handle the cases where:
- User wants to configure scarb on their own - We should allow disabling installing scarb by an optional argument. Additionally we could do some automatic detection of scarb installation.