Rudder

The Technique Enforce a file content allow to edit zones in file, and to migrate lines from outsinde the zone inside the zone (to ensure that we don't have duplicated lines)
However, this does not work as expected as:
- addition of lines are handledline by line (separately)
- migration work on a block of line

So we can end up with duplicated line where we would expect lines to be migrated

The reason behind is that agent handles line insertion on line per line (unless specific parameter is set), but deletion as a block (and there is no modifier:/)

(same ticket as #6389 but for branch 3.0)