Option to set number of frames shown in graph/histogram

[CyberShadow]

Currently this is a static array:

MangoHud/src/overlay.h

Line 59 in 425b98a

struct frame_stat frames_stats[200];

Graphs are then drawn using ARRAY_SIZE of that array.

Would be nice if this limit was configurable instead of hard-coded to 200.

Use case: I'm trying to visually demonstrate a performance issue which manifests as stable high FPS -> ~5 seconds of unstable FPS -> stable low FPS.

[flightlessmango]

closing as duplicate of #700