Improve the description of server.xml error when using the BIN upgrade method

Problem

When using the BIN installer to perform an upgrade to Jira Data Center 9.12., users may see the following error if they have customizations in the server.xml:

Your installation of Jira Software 9.12.1 is now ready.
ERROR: Unresolved i18n key "finish.serverxml.possible.change"
Custom modifications 
Your previous Jira installation contains customisations (eg server.xml) that must be manually transferred. 
Refer to our documentation more information: https://confluence.atlassian.com/adminjiraserver/upgrading-jira-manual-938846939.html 
Finishing installation ...  

Suggested Solution

Change the error message in a way that doesn't imply that there is a partial failure with Jira and provide details on what changes to the server.xml from before and after the upgrade that weren't performed.

Why This Is Important

The error message may have customers think that the upgrade may have partially failed, which can lead to concerns of whether their Jira instance would be fully functional.

Workaround

None at the moment.