Worklog Cache Limit is no longer used and can cause OutOfMemoryError when loading Classic Boards

After update the JIRA Agile plugin to the latest version, JIRA Agile Classic board is affected by the changes below and hence it become unusable.

Step to reproduce

1. Upgrade JIRA Agile to 6.3.8 or higher
2. Use Classic Boards on a large project with lots of issues and worklogs

Observations

• After upgrade, Worklog Cache Limit under JIRA Agile Configuration will be reset to 0 instead of the default value 20000.
• The field also cannot be edited and there is no way to change the Worklog Cache Limit value
• This caused JIRA to consume huge amount of memory and hence caused JIRA to have performance issues.

Work around

• Limit the number issues shown in the classic board using Context and Filter
• Avoid using nested version whenever possible
• Release inactive version