Ability to delete all branches that have been merged since a given date
### Description At the moment we have a Delete button to delete **all** the branches that have been merged to master. However, this action is all or nothing. What if we could only delete branches older than a specific date to allow a fine grain management of the branches? Companies might want to keep at least one year of branches, merged or not, in their projects, and remove the rest. ### Description * When clicking on the Delete merged branches button, display a panel asking * Delete all the branches * OR * Delete all branches before DATE
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