JIRA API should handle renamed users better

Summary

If a user is renamed, with:

• New username stored in cwd_user.user_name
• Original username stored in app_user.user_key

JIRA API may not be able to find the user in many cases. It seems some API methods/endpoints use user_name, while the others use user_key, in an inconsistent manner.

Known bugs

• JRASERVER-36642 - After renaming users in JIRA, worklogs do not expand author correctly in REST API
• JRASERVER-67262 - Updating roles through REST API did not work using username

Suggestion

Improve JIRA API to handle renamed users in a more consistent manner, and have this documented properly in the API docs.