No data displayed for Usertask reports in C8

Brief summary of the bug. What is it ? Where is it ?

Usertask count and duration reports display no data in Optimize C8 (tested in CCSM and SaaS).

Steps to reproduce:

1. Start Optimize in CCSM or SaaS
2. Deploy a process with some userTasks in it
3. Start an instance, claim and complete at least one userTask
4. Open Optimize and build a usertask duration or a usertask count report on this definition

Actual result:

No data is displayed in Optimize

Expected result:

Optimize should display data on usertask count or usertask total duration.

Notes

• Note that work and idle usertask duration reports are not supported in C8, but total usertask duration reports should be available.
• This may need backported to older C8 Optimize versions.
• as a workaround, it is possible to create flownode duration reports with a flow node selection filter only selecting usertasks, which basically visualised the same data

Hint:
Having had a quick look in the BE it could be that this occurs because we do not set any "userTaskNames" on the definition DTO when importing a definition from a ZeebeProcessDefinitionRecordDto. This is more or less a guess for now though, would need to be confirmed with more in depth debugging. 
Also, in SaaS these reports work fine for the customer onboarding data, but not for data from a manually deployed process. Note that in the customer onboarding definition json, we do have userTaskNames set which supports my above suspicion that this could be the cause.

Testing notes:

• Follow the steps to reproduce for both CCSM and SaaS and confirm data is displayed correctly in Optimize report in all available visualisations.
• If the fix was backported the same needs tested for the other affected versions
• we seem to have overlooked this in our regression tests, once we know what kind of setup causes this it could be worth considering if regression test instructions can be improved