Bulk Move with sub-tasks can timeout on validations

Issue Summary

When doing the bulk change and choosing the move issues operation (for when you want to change project or issue type). The procedure is likely to timeout in the validation stage if:

• You're moving sub-tasks
• The instance has a lot of custom fields (on my test the instance had around 500 custom fields).
• If there are too many parent issues from the sub-tasks filtered (Jira does 1 validation for each parent from sub-tasks in the bulk) - I tested with 30 different parents.

Steps to Reproduce

1. Create a lot of custom fields
2. Create a lot of parent issues and sub-tasks for each
3. Attempt to perform a Bulk Change using the Move option

Expected Results

Jira should be able to perform a bulk with 1000 issues

Actual Results

Even with very few issues, the procedure times out in one of the validation stages.

Workaround

Use bulk edit when possible or, reduce the bulk change scope until it works.

Notes

I recorded a video showing this https://share.getcloudapp.com/GGuA0EB5

We can see through the network tab that GET /secure/views/bulkedit/BulkMigrateSetFields!default.jspa exceeds the 60s threshold, ending up in a timeout.