[FEATURE] Use local config files when using dry-run mode

I'll mark this one as a **feature** but I really think it should be considered a **bug**.

### Issue

I was trying to diagnose my `release-please` setup using the `dry-run` mode:
```sh
npx release-please release-pr --token=XYZ --repo-url=XYZ --debug --dry-run
```

The thing is, I've spent hours trying to understand why it was not reflecting the modifications I was making in my local `release-please-config.json` and `.release-please-manifest.json`.

I even try specifying the files in the command itself... and that's when I realized that the actual files that are used are the ones on the repository and not the ones in my local project. Which feels completely not intuitive for a dry run.

### Feature request

Make use of the local config files when using the `dry-run` mode.