RFR: 1683: The force push notifier needs an overhaul

[Zhao Song]

On Tue, 22 Nov 2022 21:57:58 GMT, Zhao Song <zsong at openjdk.org> wrote:

> A user reported a bug related with the force-push notification. Erik investigated it and found the implementation of this notification should not be in the `PullRequestBranchNotifier`. Also, users preferred to not get force-push notification if the force-push happens when the pr is in draft state.
> 
> In this patch, the implementation of checking force-push and notifying user are moved to `CheckWorkItem`. Also, force-pushing or rebasing a draft pr will not warn user any more.

My current implementation has a bug. If a user force-pushes or rebases when the pr is in ready state, and then he converts the pr to draft state very quickly, in such a case,  our pullRequestBot won't have enough time to send warning, and then user will never get the notification of this force-push or rebase.

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PR: https://git.openjdk.org/skara/pull/1426