Improve the performance when changing the FixVersion in the Test Execution

Changing the FixVersion field of multiple Test Executions can cause timeouts, showing a "Communications Breakdown" warning message in the UI.

Steps to replicate (Example)

Step	Result
Created 5 requirements
Assigned versions randomly to the Requirements
Created 400 Tests where each one is "testing" 5 requirements
Created 1 Test Plan with all the Tests and Test Executions
Created 12 Test Executions (using a random FixVersion), where each one has linked 400 Tests
Starting changing the FixVersion of each Test Execution sequentially in the UI

The strategy used for Xray custom fields:

Environment - Jira 8.6.0 - Xray 4.3.5