[Chore] Change default storage duration to 24 months

[nwittstruck]

Description

The current default storage duration is 12 months, except for recordings. We want to change the default storage duration (exept for recordings) to 24 months.
Some QR-Codes used in school classes will be only accessed once a year. We don't want to delete them too early, but allow for a usage in the next school year as well. Therefore, we'll change the default to 24 months.

We don't want to change the deletion date of existing codes.

Checklist

• Change default storage duration to 24 months for all codes except recordings
• Change storage duration of 36 months to 48 months for
• Change deletion notice