Replace active users map with in-memory key-value store

[ikovac]

This PR: Active users map is replaced using key-value in-memory storage. Supported providers:

• lru-cache
• redis

QA note:

• this PR affects the concurrent element editing and the repository tracker of active users.
• in order to test it using Redis store, Docker needs to be installed on your system.
• start docker
• run: docker run --name redis -p 6379:6379 redis
• edit redis store option in .env if needed
• feel free to ping me if you have any question :)

[kjuej]

@ikovac @MiroDojkic Seems to be working as expected!