plugin XEP-0470: fix autocreate in `create_attachments_node`: Due to config check, `create_attachments_node` was failing when the target node was not already existing. However, this is the case when an item is published and `autocreate` is expected, thus the node is now created if not already existing and new `autocreate` argument is set.

syntax: glob
*.pyc
*.pyv
*.swp
*.swo
tags
twistd.log
twistd.pid
bridge_constructor/generated
tests/e2e/report*
_trial_temp/
sat.egg-info
*.un~
dist
MANIFEST
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ctags_links/
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.pytest_cache
env/
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libervia_backend.egg-info/
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twisted/plugins/dropin.cache