Check KPI plots if t_ref is added later

@benjamin.tallarek There seem to be a bug in the process of plot-generation. In Detail:

During the KPI review in summer, I found that the KPI result for DKFZ Filesender was more than 60. As this service is not the most popular one, it didn't make sense. After discussing with Uwe J., we found out that this was because of the rapid growth in the first days. The solution was, to define a T_referenz. This did change the overall KPI. Unfortunately it didn't change the related plots.

• T_referenz corrected to 1.1.2024, issue
• seems that T_referenz is not shown in the related plots.

Can you check, please?