Explore executing a default game mode config

[rtxa]

I'm thinking of adding a gamemode_default.cfg which will be executed when we switch of game mode.

This will avoid the need of resetting all the cvars by yourself on your game mode config.

Possible issues are players voting custom options like mp_timelimit and losing the changes on map change, but this should be adressed by online resetting on game mode switch.

Not sure if we can add more things like a _pre and _post config.

[rtxa]

We should not worry about custom plugins adding new game mode commands or custom gamemodes added, in that case administrator can edit gamemode_default.cfg to add those cvar to reset after map change.