[TASK] Protocol-ink! vanchor relayer support

[dutterbutter]

Overview

We have support for the Substrate/EVM vanchor, therefore it shouldn't be terribly different to integrate support for the protocol-ink! vanchor.

Checklist

• [ ] Add a handler for the protocol-ink! vanchor, using the other handlers as a reference.
• [ ] Add a test for it as an integration test.
• [ ] Add inline documentation to the file and wherever else is relevant if there's missing docs.