UnreleasedVersions() is slow on large instances

Summary

Loading time for Kanban board with default work subfilter is longer.
Default work subfilter with UnreleasedVersions():

fixVersion in unreleasedVersions() OR fixVersion is EMPTY

Calls to /rest/greenhopper/1.0/xboard/work/allData.json are more slow with default work subfilter.

Environment

• Instances with large number of Versions are affected, example: 10k+

Steps to Reproduce

1. Load board

Expected Results

Loading board doesn't degrade with number of version in other project (in whole JIRA)

Actual Results

Loading board takes longer when there is a higher number of version in other project (in whole JIRA).

Notes

See related KB: Kanban board loading is slow

Some improvements have already been done in GHS-9611, JRA-38883, JRASERVER-62666

Original data from user

Here are some system stats

Total versions: 23792
Of the total, 20616 are *unreleased*.

JIRA issues: 1.5 million
Projects: 660

Here's a before and after load time in seconds when we delete the work subfilter:

11.7050  https://jira/rest/greenhopper/1.0/xboard/work/allData.json 
11.3350  https://jira/rest/greenhopper/1.0/xboard/work/allData.json 

--- delete work subfilter ---

3.0680  https://jira/rest/greenhopper/1.0/xboard/work/allData.json 
3.1440  https://jira/rest/greenhopper/1.0/xboard/work/allData.json 
3.0290  https://jira/rest/greenhopper/1.0/xboard/work/allData.json 
3.1320  https://jira/rest/greenhopper/1.0/xboard/work/allData.json 

Workaround

• Delete Kanban board sub-filter if you don't need versions
• If you need version, add specific project(s) related to JQL filter for the board into unreleasedVersions function

  fixVersion in unreleasedVersions(ProjA, ProjB) OR fixVersion is EMPTY