Make local room events cache size configurable via Element-Android app UI

**Is your feature request related to a problem? Please describe.**
The problem is that we have only little part of last events (should be 30, but looks random, sometimes only one visible event!) preloaded in timeline of most rooms, and we need to watch the spinner always, when make a little scroll up, especially on slow servers or low bandwidth.

**Describe the solution you'd like**
I want to have always preloaded in local device cache at least 200 (or even more, maybe 500+, depend on total cache size) last events per each joined room, to view it instantly, without requiring them each time from server, and even when I offline. But for some users this cache can be too large, so good to make this value configurable.

Best solution is to add the configuration option for configure needed size of room events local cache, with name like "Size of recent rooms message cache".

Ideally, if it will be in "`m.message` count per room" dimensions, but the total cache size in events or bytes as first quick implementation will be good too.

And will be best if we can configure it for each room type individually, eg 500 for "People", 400 for "Rooms", 100 for "Low priority", and 20 for muted rooms.