Caption file is saved several times for the same language

Could be because several AWS enrichers are configured and the DocumentTranscribed called several times, each time adding the caption file.

https://github.com/nuxeo/nuxeo-ai/blob/56cb880e87616d4e0e6b255b5ce0f5479564aa7b/addons/nuxeo-ai-aws-core/src/main/java/org/nuxeo/ai/listeners/DocumentTranscribed.java#L136

Should use the set method instead of add (add doesn't replace the element at the index and instead shifts all the elements to the right)