[feature] Multiple User Accounts

**Version and OS**
linux/docker

**Is your feature request related to a problem? Please describe.**
I would like to be able to share the features of changedetection with friends and family, but it currently only has a single password to login.

**Describe the solution you'd like**
It would be amazing to be able to have multiple user accounts

The issue names no files, tests, or entry points. Start by surveying the existing single-password login flow and the Linux/Docker deployment setup, then clarify the account and access requirements; done means changedetection supports multiple user accounts rather than one shared password.

Written by the indexing model from the issue text.