PTEUDO-2363: Implement AWS provider

[bfabricio]

tl;dr:

While this may seem like a medium refactor, the core change is simply moving awsprovider.go behind the new provider interface, with some improvements in the code flow.

Design decisions:

• The provider package is responsible for provisioning databases using a given provider (crossplane aws, crossplane gcp, cloudnative-pg). It remains independent of the controller logic, ensuring a clear separation of concerns. The provider implementations should stay clean, avoiding passing references to DatabaseClaim or other internal controller details.
• Dependency injection is used to connect the provider with the controller reconciler.
• Feature toggling: Decommissioning the old logic is optional. The new provider can be enabled behind a feature flag for safety. Once all providers are implemented, we can fully remove the old logic.
• The overall structure remains similar to what we had, with adjustments to simplify and improve testability.

Testing:

This refactor significantly improves test coverage. Since the provider logic is now decoupled from the reconciler, we can move from almost 0% unit test coverage to full testability of interactions with Crossplane or other providers. Also, we can mock the provider in DatabaseClaimReconciler tests to precisely validate what is being passed.

Along with increased unit test coverage we must ensure the crossplane aws resource creation/update behavior remains unchanged, that can be done trough regression.

Missing:

• We have some provider operational tagging code which is deeply entangled with the controller reconciler logic. The code seems to be pretty simple, we tag decommissioned databases with were migrated with operational-status: inactive
• Finish unit tests, discuss more complex test scenarios