Introduce multipart works

[fellowseb]

Proposed changes

Aftermath of the addition of the is_multipart flag on the to_processed client-python API. The intent is to better handle the completed status of works that use multiple bundles.

• Updates connectors documentation and templates
• Updates connectors that send multiple bundles to use the new is_multipart=True option
• Updates connectors to make sure they call to_processed in a finally block

/!\ This work is still in draft as we may have identified a case that isn't handled well: the case where the worker does the bundle splitting itself.

Related issues

Checklist

• I consider the submitted work as finished
• I have signed my commits using GPG key.
• I tested the code for its functionality using different use cases
• I added/update the relevant documentation (either on github or on notion)
• Where necessary I refactored code to improve the overall quality

Further comments