[GitHub App] - Option to disable PR preview comments

> This should have been a feature request, my apologies.

### Before opening, please confirm:

- [X] I have checked to see if my question is addressed in the [FAQ](https://github.com/aws-amplify/amplify-console/blob/master/FAQ.md).
- [X] I have [searched for duplicate or closed issues](https://github.com/aws-amplify/amplify-console/issues?q=is%3Aissue+).
- [X] I have read the guide for [submitting bug reports](https://github.com/aws-amplify/amplify-console/blob/master/CONTRIBUTING.md).
- [X] I have done my best to include a minimal, self-contained set of instructions for consistently reproducing the issue.

### App Id

Not relevant

### Region

us-east-1

### Amplify Console feature

Previews

### Describe the bug

I love the new GitHub integration to notify users about the PR preview! This was a huge issue for our developers because it's relatively inconvenient to have to sign in to AWS to access the info on the Amplify console.

However, because our team needed this earlier, I wrote custom postBuild scripts that performed a superset of functionality including a link to the build console and build size diffs for Next.js (hit me up if you wanna learn how I did it 😄)

Because of this, the GitHub App adds noise since two comments get created per PR.

### Expected behavior

There should be a setting, per PR preview branch(?), that disable this GitHub App functionality.

### Reproduction steps

1. Link a GitHub repository
2. Set up PR previews
3. Create a PR

### Build Settings

_No response_

### Additional information

_No response_

Review the GitHub integration and PR preview flow, beginning with the Previews feature and the linked FAQ.md and CONTRIBUTING.md guidance. Determine how a per-branch setting should control generated preview comments, then verify the behavior by linking a repository, enabling PR previews, and creating a pull request.

Written by the indexing model from the issue text.