feat(automation): rebase instance development branch if possible

[lutangar]

This is an automation feature to help reduce differences with the dev branch as much as possible.

The idea is to keep an open (Draft) PR with the instance-development-branch label for each instances at all time :

• if the dev branch is updated, the instance branch is automatically updated
• when you want it merged, remove the Draft status.

We will probably need to give this more thoughts... but for now we probably need to :

• reopen the same Draft PR right after it was merged...

We might be playing with tags next... have you already ?