The console command you want is simple enough it is:
endround
While this may seem obvious in hindsight, it took me a long time to realize this myself. I only found it after mindlessly scrolling through cvars for awhile when I was bored.
If you want to have an entity to trigger this then add in the point entity point_servercommand to your map with the output Command and the parameter endround. One of the main advantages that this cvar has over similar ones (like mp_restartgame) is that all the player's scores remain intact and mp_timelimit isn't reset.
