Add option to toggle server caching

I recently noticed that discord has been using an enormous amount of RAM when switching between servers (it got up to 2GB for me even with hardware acceleration off) so I contacted support, and I've been told it might be caused by the desktop app caching the servers to reduce loading time of already viewed messages.

It would be nice if we could toggle this on or off in the settings, for those who would rather have a bit slower loading times than discord using all of the memory