Add a setting that allows draft PRs to account towards a users limit [GA]

### Value Prop
Repository maintainers can now configure draft pull requests to count toward a user's pull request limit, closing a loophole that allowed contributors — or automated agents — to open unlimited draft pull requests. This gives teams stronger control over their contribution workflows, reducing unwanted noise from notifications, unnecessary CI runs, and a cluttered pull request list. Whether you're managing a large open source project or enforcing contribution policies in an enterprise environment, this setting helps your limits actually work as intended.

### Expected Outcome
Teams that rely on pull request limits to manage spam or enforce contribution policies will have a more effective tool that covers both open and draft pull requests. By making this behavior configurable, maintainers can tailor the setting to their repository's needs without impacting teams who prefer the existing behavior.

The issue describes a repository setting that changes whether draft pull requests count toward a user's pull request limit, but it names no implementation files, tests, or entry points. Start by locating the existing pull request limit behavior and its repository configuration, then define the setting, update the limit calculation, and verify both enabled and disabled behavior.

Scritto dal modello di indicizzazione a partire dal testo della issue.