[IX] - Long requests timeout

[txau]

This is a known problem in Uwazi, long synchronous requests that require heavy backend processes may timeout on the client before the backend finishes.

This is the case for the step "Sending labeled data" for IX. The user receives an undefined "An error has occurred" on the UI, but actually is just the UI waiting for the server response. The process actually finishes properly on the backend.

A quick fix with no side effects could be making that request asynchronous and not have the client wait for the labeled data to be sent.

Edit: this is also typical when saving templates. If we are performing a modification to a template that has many entities associated, the request can timeout before the operation is finished giving a UI error and misleading users, since there is no error, just a timeout.