Move head branch of empty rebase PRs

[premun]

Problem

We have the following situation:

1. We have some commits on the target branch:

   gitGraph
       commit
       commit
       commit
   

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2. We create a codeflow PR that has a conflict, so it only creates the "initializer" empty commit, like so:

   gitGraph
       commit
       commit id: "PR base commit"
       branch prBranch
       commit id: "Initial PR commit"
       checkout main
       commit
   

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3. Now no one tends to the PR and more commits merge into the target branch

   gitGraph
       commit
       commit id: "PR base commit"
       branch prBranch
       commit id: "Initial PR commit"
       checkout main
       commit
       commit id: "new commit #1"
       commit id: "new commit #2"
       commit id: "new commit #3"
   

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4. Now if the service wants to flow new commits, the PR branch already exists and can't be rebased properly.

Goal

When no commits were flown yet, we should instead recreate the PR branch like it would be at the top of the main branch.

gitGraph
    commit
    commit
    commit
    commit id: "new commit #1"
    commit id: "new commit #2"
    commit id: "new commit #3"
    branch prBranch
    commit id: "Initial PR commit"

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But, we can't do it during the flow because then the dev would need to force-push.
Instead, I think whenever the service flows new build, it should check if it actually made any commits so far and if not, it should rebase+force-push.