Keep session cookie during 5 days

## Feature Request

**Is your feature request related to a problem or unsupported use case? Please describe.**
Users complain they have to login everyday.
Right now we keep the session for only 12 hours : https://github.com/suitenumerique/docs/blob/main/src/backend/impress/settings.py#L466

**Describe the solution you'd like**
Let's keep the session cookie for 5 days.