Improve local development and testability

[andreasohlund]

To make it easier to build and test the action locally we should:

• Introduce a dev container similar to the oracle action
• Make the region lookup overridable since it won't work locally
• Add support for npm run dev to make sure that changes are properly recompiled automatically
• Evaluate if switching to typescript and pulumi would be helpful, see this spike for the oracle setup action for an example