[Feature]: ADK Go support

### Pre-flight Checklist

- [x] I have searched existing issues and this hasn't been requested yet.

### Problem or Motivation

There is existing middleware integrations for ADK's Python and Typescript implementations. We'd need support for the Go implementation. Is there appetite for this to be part of this repo? We'd be willing to drive initial implementation.

### Proposed Solution

There is a Go SDK already. This work would be based on this and thus increase the degree of testing and contribute eventual fixes.

There is a decision to be made on whether to use similar custom implementations as done for Python, e.g. the custom pending tool workarounds, or whether to leverage ADK-native features for HITL/long-running/confirmation. There is a reference for many patterns already in `integrations/community/genkit/go`.

### Alternatives Considered

_No response_

### Additional Context

_No response_