rename puppet-tails:update_weblate_git.py → merge_canonical_changes.py

The name update_weblate_git.py doesn’t reflect anymore what the script is doing, that’s why a rename makes sense to reflect what the script is doing.

If the script is renamed, also the documentation(#15086 (closed)) needs to be updated.

Original created by @Hefee on 17129 (Redmine)

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