[KV Feedback]: Access default database outside of master branch

### 🔍

- [x] Did you search for existing issues?

### Type of feedback

Feature request

### Description

I have a production deployment that does not use Deno KV yet. But my `development` branch does. I can't create a preview deployment for my `development` branch because the default database is only available on the `master` branch.

Is it possible to make it available on other branches?

### Steps to reproduce (if applicable)

1. Create a Deno API.
2. Deploy to Deno Deploy.
3. Create a new branch with a KV implementation.
4. Make preview deployment.

### Expected behavior (if applicable)

Preview deployment is successful and creates a KV instance.

### Possible solution (if applicable)

_No response_

### Additional context

_No response_