Add a configurable memory limit to the torrent repositories

[josecelano]

From: #567

Relates to:

• Consider getting rid of the torrents cleanup job in favour of a torrents priority map with a max size #499
• Tracker restarted when memory is full #566
• Use dashmap for torrent in memory storage instead of the std hashmap #565

@mickvandijke was working on adding a memory limit to one of the torrent repository implementations:

#645

It was implemented only for one of the repos (DashMap).

We should consider if we want to implement it for all the repositories.

If you want to know what a torrent repository is, check this discussion: #774